auto pick up buble-loader if it is present

Author: yyx990803

lib/loader.js

@@ -15,12 +15,15 @@ var styleRewriterPath = normalize.lib('style-rewriter')
 var styleLoaderPath = normalize.dep('vue-style-loader')
 var hotReloadAPIPath = normalize.dep('vue-hot-reload-api')
 
-var hasBabel = true
+var hasBabel = false
 try {
-  require('babel-loader')
-} catch (e) {
-  hasBabel = false
-}
+  hasBabel = !!require('babel-loader')
+} catch (e) {}
+
+var hasBuble = false
+try {
+  hasBuble = !!require('buble-loader')
+} catch (e) {}
 
 var rewriterInjectRE = /\b(css(?:-loader)?(?:\?[^!]+)?)(?:!|$)/
 
@@ -55,7 +58,7 @@ module.exports = function (content) {
   var defaultLoaders = {
     html: templateCompilerPath + '?id=' + moduleId,
     css: styleLoaderPath + '!css-loader' + (needCssSourceMap ? '?sourceMap' : ''),
-    js: hasBabel ? 'babel-loader' : ''
+    js: hasBuble ? 'buble-loader' : hasBabel ? 'babel-loader' : ''
   }
 
   // check if there are custom loaders specified via