docs: Update CONTRIBUTING.md (#1495)

Author: cleptric

CONTRIBUTING.md

@@ -18,7 +18,7 @@ If you feel that you can fix or implement it yourself, please read on to learn h
 - Clone the `sentry-php` repository and prepare necessary changes.
 - Add tests for your changes to `tests/`.
 - Run tests and make sure all of them pass.
-- Submit a pull request, targeting the `develop` branch if you added any new features. For bug fixes of the current release, please target the `master` branch instead.
+- Open a pull request.
 
 We will review your pull request as soon as possible.
 Thank you for contributing!