Update default branch from master to main (#589)

Author: sujaygarlanka

.github/ISSUE_TEMPLATE/config.yml

@@ -1,7 +1,7 @@
 blank_issues_enabled: false
 contact_links:
   - name: SDK documentation
-    url: https://github.com/box/box-python-sdk/tree/master/docs
+    url: https://github.com/box/box-python-sdk/tree/main/docs
     about: Before creating an issue, I have checked that the SDK documentation doesn't solve my issue.
   - name: API documentation
     url: https://developer.box.com/docs

.travis.yml

@@ -3,7 +3,7 @@ language: python
 
 branches:
     only:
-        - master
+        - main
         - "1.5"
 
 cache:

CONTRIBUTING.rst

@@ -84,7 +84,7 @@ Before sending a pull request, rebase against upstream, such as:
 .. code-block:: console
 
     git fetch upstream
-    git rebase upstream/master
+    git rebase upstream/main
 
 This will add your changes on top of what's already in upstream,
 minimizing merge issues.
@@ -106,4 +106,4 @@ down issues.
 
 Finally, please add a note in HISTORY.rst under the Upcoming section detailing what's new in your change.
 These will become the release notes for the next release.
-In addition, feel free to add yourself to AUTHORS.rst if you aren't already listed.
+In addition, feel free to add yourself to AUTHORS.rst if you aren't already listed.