main vs master

Co-authored-by: Jaap van Otterdijk <jaap@ijaap.nl>

Author: Crell

CONTRIBUTING.md

@@ -14,7 +14,7 @@ We accept contributions via Pull Requests on [Github](https://github.com/php-fig
 
 - **Consider our release cycle** - We try to follow [SemVer v2.0.0](http://semver.org/). Randomly breaking public APIs is not an option.
 
-- **Create feature branches** - Don't ask us to pull from your master branch.
+- **Create feature branches** - Don't ask us to pull from your main branch.
 
 - **One pull request per feature** - If you want to do more than one thing, send multiple pull requests.