Merge pull request #2846 from pmvieira/Fix-contibuting-instructions

Correcting the branch name as per issue-2843

CONTRIBUTING.md

@@ -4,7 +4,7 @@
 
 1. Fork the Slim Framework repository
 2. Create a new branch for each feature or improvement
-3. Send a pull request from each feature branch to the **develop** branch
+3. Send a pull request from each feature branch to the **4.x** branch
 
 It is very important to separate new features or improvements into separate feature branches, and to send a
 pull request for each branch. This allows me to review and pull in new features or improvements individually.