Update CONTRIBUTING.md

Fix numbering

Author: stanleyw

CONTRIBUTING.md

@@ -16,7 +16,7 @@ Our goal is to keep `master` stable, but there may be changes that your applicat
 We actively welcome your pull requests. When we get one, we'll run some Parse-specific integration tests on it first. From here, we'll need to get a core member to sign off on the changes and then merge the pull request. For API changes we may need to fix internal uses, which could cause some delay. We'll do our best to provide updates and feedback throughout the process.
 
 1. Fork the repo and create your branch from `master`.
-4. Add unit tests for any new code you add.
+2. Add unit tests for any new code you add.
 3. If you've changed APIs, update the documentation.
 4. Ensure the test suite passes.
 5. Make sure your code lints.