chore(package): update babel-core to version 6.7.2

http://greenkeeper.io/

package.json

@@ -9,7 +9,7 @@
   "license": "Apache-2.0",
   "devDependencies": {
     "babel": "~6.3.26",
-    "babel-core": "~6.4.0",
+    "babel-core": "~6.7.2",
     "babel-loader": "~6.2.0",
     "babel-preset-es2015": "~6.3.13",
     "babelify": "~7.2.0",