chore(package): update babel-core to version 6.20.0

https://greenkeeper.io/

Author: greenkeeperio-bot

Diff for: package.json

@@ -35,7 +35,7 @@
     "prepublish": "gulp build"
   },
   "dependencies": {
-    "babel-core": "^6.18.2",
+    "babel-core": "^6.20.0",
     "babel-eslint": "^7.1.0",
     "babel-register": "^6.18.0",
     "babel-plugin-syntax-class-properties": "^6.13.0",