Docs: Updates Angular commit conventions link in Contributing.md (#472)

* docs(contributing): Updates link to the new link for Angular commit convention

* docs(contributing): updates Angular commit convention link

updated to match the link pattern used on the readme

Author: slkennedy

CONTRIBUTING.md

@@ -5,7 +5,7 @@
 You consider contributing changes to commitizen – thank you!
 Please consider these guidelines when filing a pull request:
 
-*  Commits follow the [Angular commit convention](https://github.com/angular/angular.js/blob/master/CONTRIBUTING.md#-git-commit-guidelines)
+*  Commits follow the [Angular commit convention](https://github.com/angular/angular.js/blob/master/DEVELOPERS.md#-git-commit-guidelines)
 *  JavaScript is written using ES2015 features
 *  2 spaces indentation
 *  Features and bug fixes should be covered by test cases