avoid duplicate -loader for custom langs

Author: yyx990803

lib/loader.js

@@ -152,13 +152,21 @@ module.exports = function (content) {
           return defaultLoaders.html + '!' + templateLoaderPath + '?raw&engine=' + lang + '!'
         case 'styles':
           loader = addCssModulesToLoader(defaultLoaders.css, part, index)
-          return loader + '!' + rewriter + lang + '-loader!'
+          return loader + '!' + rewriter + ensureBang(ensureLoader(lang))
         case 'script':
-          return injectString + lang + '-loader!'
+          return injectString + ensureBang(ensureLoader(lang))
       }
     }
   }
 
+  function ensureLoader (lang) {
+    if (!/-loader$/.test(lang)) {
+      return lang + '-loader'
+    } else {
+      return lang
+    }
+  }
+
   function getSelectorString (type, index) {
     return selectorPath +
       '?type=' + type +