Fix an editing artifact in CONTRIBUTING.md

Author: dkhalanskyjb

CONTRIBUTING.md

@@ -33,7 +33,6 @@ We love PRs. Submit PRs [here](https://github.com/Kotlin/kotlinx.coroutines/pull
 However, please keep in mind that maintainers will have to support the resulting code of the project,
 so do familiarize yourself with the following guidelines. 
 
-* Before introducing a code change,
 * All development (both new features and bug fixes) is performed in the `develop` branch.
   * The `master` branch contains the sources of the most recently released version.
   * Base your PRs against the `develop` branch.