Update CONTRIBUTING.md

Author: Justin Martin

CONTRIBUTING.md

@@ -1,6 +1,6 @@
 ## Please Contribute!
 
-* I would like to add unit tests before modifying any of the comparing/highlighting logic
 * Please make sure there is an issue reported before creating a pull request
+* Pull requests should be directed at fixing a previously reported issue.
 * Please follow similar syntax conventions
 * setup steps are [in the readme](https://github.com/justspamjustin/online-json-diff/blob/master/README.md#setup)