Update branch names in README and CONTRIBUTING to main

CONTRIBUTING.md

@@ -70,10 +70,10 @@ can skip this section.
 
 Twirp uses Github releases. To make a new release:
 
-1.  Merge all changes that should be included in the release into the master branch.
+1.  Merge all changes that should be included in the release into the main branch.
 2.  Update the version constant in `internal/gen/version.go`. Please respect [semantic versioning](http://semver.org/): `v<major>.<minor>.<patch>`.
 3.  Run `make test_all` to re-generate code and run tests. Check that generated test files include the new version in the header comment.
-4.  Add a new commit to master with a message like "Version vX.X.X release" and push.
+4.  Add a new commit to main with a message like "Version vX.X.X release" and push.
 5.  Tag the commit you just made: `git tag vX.X.X` and `git push origin --tags`.
 6.  Go to Github https://github.com/twitchtv/twirp/releases and "Draft a new release".
 7.  Make sure that all new functionality is properly documented, on code comments, PR description, and include links and/or upgrade instructions on the release. For example the [v7 release](https://github.com/twitchtv/twirp/releases/tag/v7.0.0). Minor releases can just include a link to the PR/PRs that were merged included into the release.
@@ -86,6 +86,6 @@ opensource-codeofconduct@amazon.com with any additional questions or comments.
 
 ## Licensing
 
-See the [LICENSE](https://github.com/twitchtv/twirp/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/twitchtv/twirp/blob/main/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

@@ -1,4 +1,4 @@
-![Twirp Logo](./logo.png) [![Build Status](https://travis-ci.org/twitchtv/twirp.svg?branch=master)](https://travis-ci.org/twitchtv/twirp) [![Go Report Card](https://goreportcard.com/badge/github.com/twitchtv/twirp)](https://goreportcard.com/report/github.com/twitchtv/twirp) [![GoDoc](https://godoc.org/github.com/twitchtv/twirp?status.svg)](https://godoc.org/github.com/twitchtv/twirp)
+![Twirp Logo](./logo.png) [![Build Status](https://travis-ci.org/twitchtv/twirp.svg?branch=main)](https://travis-ci.org/twitchtv/twirp) [![Go Report Card](https://goreportcard.com/badge/github.com/twitchtv/twirp)](https://goreportcard.com/report/github.com/twitchtv/twirp) [![GoDoc](https://godoc.org/github.com/twitchtv/twirp?status.svg)](https://godoc.org/github.com/twitchtv/twirp)
 
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