Only load .json files from locale directories

This opens up the possibility of putting READMEs or what have you
inside locale directories, and will avoid problems if system files or
folders end up in the locales.

src/i18n.js

@@ -11,6 +11,7 @@ var loadTranslations = function(locale){
   var files = fs.readdirSync(path.join(localePath, locale));
   translations[locale] = {};
   _.each(files, function(file){
+    if(path.extname(file) !== '.json') return;
     _.merge(translations[locale], require(path.join(localePath, locale, file)));
   });
 };