chore(package): update babel-core to version 6.18.0

https://greenkeeper.io/

Author: greenkeeperio-bot

package.json

@@ -32,7 +32,7 @@
   ],
   "devDependencies": {
     "babel-cli": "6.16.0",
-    "babel-core": "6.16.0",
+    "babel-core": "6.18.0",
     "babel-preset-es2015": "6.16.0",
     "babel-preset-stage-0": "6.16.0",
     "rimraf": "2.5.4"