chore(package): update babel-preset-es2015 to version 6.18.0 (#2315)

https://greenkeeper.io/ [skip ci]

Author: greenkeeperio-bot

package.json

@@ -59,7 +59,7 @@
   },
   "devDependencies": {
     "babel-plugin-transform-class-properties": "^6.16.0",
-    "babel-preset-es2015": "^6.16.0",
+    "babel-preset-es2015": "^6.18.0",
     "chai": "^3.2.0",
     "del": "^2.2.0",
     "grunt": "^1.0.1",