Fix link in CONTRIBUTING.md

Former-commit-id: c34e85ed

CONTRIBUTING.md

@@ -393,7 +393,7 @@ merge request:
 1.  [Newlines styleguide][newlines-styleguide]
 1.  [Testing](doc/development/testing.md)
 1.  [JavaScript (ES6)](https://github.com/airbnb/javascript)
-1.  [JavaScript (ES5)](https://github.com/airbnb/javascript/tree/master/es5)
+1.  [JavaScript (ES5)](https://github.com/airbnb/javascript/tree/es5-deprecated/es5)
 1.  [SCSS styleguide][scss-styleguide]
 1.  [Shell commands](doc/development/shell_commands.md) created by GitLab
     contributors to enhance security