chore: switch to mainline as default branch

Author: clareliguori

.mergify.yml

@@ -1,7 +1,7 @@
 pull_request_rules:
   - name: Automatically merge on CI success and review approval
     conditions:
-      - base=master
+      - base=mainline
       - "#approved-reviews-by>=1"
       - approved-reviews-by=@awslabs/developer-experience
       - -approved-reviews-by~=author
@@ -23,7 +23,7 @@ pull_request_rules:
 
   - name: Automatically approve and merge Dependabot PRs
     conditions:
-      - base=master
+      - base=mainline
       - author=dependabot[bot]
       - label=dependencies
       - status-success=Build Docker image from Dockerfile

CONTRIBUTING.md

@@ -1,17 +1,17 @@
 # Contributing Guidelines
 
-Thank you for your interest in contributing to our project. Whether it's a bug report, new feature, correction, or additional 
+Thank you for your interest in contributing to our project. Whether it's a bug report, new feature, correction, or additional
 documentation, we greatly value feedback and contributions from our community.
 
-Please read through this document before submitting any issues or pull requests to ensure we have all the necessary 
+Please read through this document before submitting any issues or pull requests to ensure we have all the necessary
 information to effectively respond to your bug report or contribution.
 
 
 ## Reporting Bugs/Feature Requests
 
 We welcome you to use the GitHub issue tracker to report bugs or suggest features.
 
-When filing an issue, please check [existing open](https://github.com/awslabs/aws-lambda-aws-lambda-container-image-converter/issues), or [recently closed](https://github.com/awslabs/aws-lambda-aws-lambda-container-image-converter/issues?utf8=%E2%9C%93&q=is%3Aissue%20is%3Aclosed%20), issues to make sure somebody else hasn't already 
+When filing an issue, please check [existing open](https://github.com/awslabs/aws-lambda-aws-lambda-container-image-converter/issues), or [recently closed](https://github.com/awslabs/aws-lambda-aws-lambda-container-image-converter/issues?utf8=%E2%9C%93&q=is%3Aissue%20is%3Aclosed%20), issues to make sure somebody else hasn't already
 reported the issue. Please try to include as much information as you can. Details like these are incredibly useful:
 
 * A reproducible test case or series of steps
@@ -23,7 +23,7 @@ reported the issue. Please try to include as much information as you can. Detail
 ## Contributing via Pull Requests
 Contributions via pull requests are much appreciated. Before sending us a pull request, please ensure that:
 
-1. You are working against the latest source on the *master* branch.
+1. You are working against the latest source on the *mainline* branch.
 2. You check existing open, and recently merged, pull requests to make sure someone else hasn't addressed the problem already.
 3. You open an issue to discuss any significant work - we would hate for your time to be wasted.
 
@@ -36,17 +36,17 @@ To send us a pull request, please:
 5. Send us a pull request, answering any default questions in the pull request interface.
 6. Pay attention to any automated CI failures reported in the pull request, and stay involved in the conversation.
 
-GitHub provides additional document on [forking a repository](https://help.github.com/articles/fork-a-repo/) and 
+GitHub provides additional document on [forking a repository](https://help.github.com/articles/fork-a-repo/) and
 [creating a pull request](https://help.github.com/articles/creating-a-pull-request/).
 
 
 ## Finding contributions to work on
-Looking at the existing issues is a great way to find something to contribute on. As our projects, by default, use the default GitHub issue labels (enhancement/bug/duplicate/help wanted/invalid/question/wontfix), looking at any ['help wanted'](https://github.com/awslabs/aws-lambda-aws-lambda-container-image-converter/labels/help%20wanted) issues is a great place to start. 
+Looking at the existing issues is a great way to find something to contribute on. As our projects, by default, use the default GitHub issue labels (enhancement/bug/duplicate/help wanted/invalid/question/wontfix), looking at any ['help wanted'](https://github.com/awslabs/aws-lambda-aws-lambda-container-image-converter/labels/help%20wanted) issues is a great place to start.
 
 
 ## Code of Conduct
-This project has adopted the [Amazon Open Source Code of Conduct](https://aws.github.io/code-of-conduct). 
-For more information see the [Code of Conduct FAQ](https://aws.github.io/code-of-conduct-faq) or contact 
+This project has adopted the [Amazon Open Source Code of Conduct](https://aws.github.io/code-of-conduct).
+For more information see the [Code of Conduct FAQ](https://aws.github.io/code-of-conduct-faq) or contact
 [email protected] with any additional questions or comments.
 
 
@@ -56,6 +56,6 @@ If you discover a potential security issue in this project we ask that you notif
 
 ## Licensing
 
-See the [LICENSE](https://github.com/awslabs/aws-lambda-aws-lambda-container-image-converter/blob/master/LICENSE) file for our project's licensing. We will ask you to confirm the licensing of your contribution.
+See the [LICENSE](https://github.com/awslabs/aws-lambda-aws-lambda-container-image-converter/blob/mainline/LICENSE) file for our project's licensing. We will ask you to confirm the licensing of your contribution.
 
 We may ask you to sign a [Contributor License Agreement (CLA)](http://en.wikipedia.org/wiki/Contributor_License_Agreement) for larger changes.

README.md

@@ -1,6 +1,6 @@
 ## AWS Lambda Container Image Converter
 
-[![Build Status](https://travis-ci.org/awslabs/aws-lambda-container-image-converter.svg?branch=master)](https://travis-ci.org/awslabs/aws-lambda-container-image-converter)
+[![Build Status](https://travis-ci.org/awslabs/aws-lambda-container-image-converter.svg?branch=mainline)](https://travis-ci.org/awslabs/aws-lambda-container-image-converter)
 
 This container image converter tool (img2lambda) extracts an AWS Lambda function deployment package from a container image (such as a Docker image).
 It also extracts AWS Lambda layers from a container image, and publishes them as new layer versions to Lambda.

img2lambda/version/version.go

@@ -3,7 +3,7 @@
 package version
 
 // Version indicates which version of the binary is running.
-var Version = "master"
+var Version = "mainline"
 
 // GitCommitSHA indicates which git shorthash the binary was built off of
 var GitCommitSHA string