bump babel version

package.json

@@ -35,7 +35,7 @@
   },
   "homepage": "https://github.com/vuejs/vue#readme",
   "devDependencies": {
-    "babel-core": "6.7.x",
+    "babel-core": "6.8.x",
     "babel-loader": "6.2.x",
     "babel-preset-es2015": "6.6.x",
     "babel-preset-es2015-rollup-vue": "1.0.x",