Fix the proptypes deprecation warning url on the "Don't Call PropTypes Warning" doc page (#9419)

* Use the same prop-types link on the warning docs page as the main proptypes doc page

* Link to repo instead

warnings/dont-call-proptypes.md

@@ -5,7 +5,7 @@ permalink: warnings/dont-call-proptypes.html
 ---
 
 > Note:
-> `React.PropTypes` is deprecated as of React v15.5. Please use [the `prop-types` library instead](https://github.com/aackerman/PropTypes).
+> `React.PropTypes` is deprecated as of React v15.5. Please use [the `prop-types` library instead](https://github.com/reactjs/prop-types).
 
 In a future major release of React, the code that implements PropType validation functions will be stripped in production. Once this happens, any code that calls these functions manually (that isn't stripped in production) will throw an error.