Merge pull request #1271 from mozilla/greenkeeper-babel-core-6.18.0

Update babel-core to version 6.18.0 🚀

package.json

@@ -190,7 +190,7 @@
   },
   "devDependencies": {
     "autoprefixer": "6.5.1",
-    "babel-core": "6.17.0",
+    "babel-core": "6.18.0",
     "babel-eslint": "7.0.0",
     "babel-gettext-extractor": "git+https://github.com/muffinresearch/babel-gettext-extractor.git#ecd85dea4553247a3cb579da817df29f381df5b9",
     "babel-loader": "6.2.5",