fix(config): prioritized package.json last when looking for config files

since package.json was prioritized first, it is always found and always used, even if it does not contain commitizen config. the other optional config files are never found as a result. this change looks for the optional files first and only lands on the package.json if the other files do not exist

fixes commitizen#478

Author: travi

src/commitizen/configLoader.js

@@ -3,7 +3,7 @@ import {loader} from '../configLoader';
 export { load };
 
 // Configuration sources in priority order.
-var configs = ['package.json', '.czrc', '.cz.json'];
+var configs = ['.czrc', '.cz.json', 'package.json'];
 
 function load (config, cwd) {
   return loader(configs, config, cwd);