docs(CONTRIBUTING.md): change type descriptions for less confusion

CONTRIBUTING.md

@@ -84,8 +84,9 @@ Must be one of the following:
 * **fix**: A bug fix
 * **docs**: Documentation only changes
 * **style**: Changes that do not affect the meaning of the code (white-space,
-  formatting, etc)
-* **refactor**: A code change that neither fixes a bug nor adds a feature
+  formatting, etc), but change the style to a more appropriate one
+* **refactor**: A code change that only improves code readability 
+  and reduced complexity, without changing any functionality
 * **perf**: A code change that improves performance
 * **revert**: Reverts a previous commit
 * **test**: Adding missing tests