renames master -> mainline

Author: steffeng

CONTRIBUTING.md

@@ -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.
 
@@ -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/aws-samples/amazon-cloudfront-access-logs-queries/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/aws-samples/amazon-cloudfront-access-logs-queries/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

@@ -88,8 +88,8 @@ If you found yourself wishing this set of frequently asked questions had an answ
 
 ### Q: How can I contribute?
 
-See the [Contributing Guidelines](https://github.com/aws-samples/amazon-cloudfront-access-logs-queries/blob/master/CONTRIBUTING.md) for details.
+See the [Contributing Guidelines](https://github.com/aws-samples/amazon-cloudfront-access-logs-queries/blob/mainline/CONTRIBUTING.md) for details.
 
 ## License Summary
 
-This sample code is made available under a modified MIT license. See the [LICENSE](https://github.com/aws-samples/amazon-cloudfront-access-logs-queries/blob/master/LICENSE) file.
+This sample code is made available under a modified MIT license. See the [LICENSE](https://github.com/aws-samples/amazon-cloudfront-access-logs-queries/blob/mainline/LICENSE) file.