chore(package): update babel-preset-stage-2 to version 6.18.0 (#371)

https://greenkeeper.io/

Author: greenkeeperio-bot

package.json

@@ -52,7 +52,7 @@
     "babel-cli": "6.18.0",
     "babel-core": "6.17.0",
     "babel-preset-es2015": "6.18.0",
-    "babel-preset-stage-2": "6.17.0",
+    "babel-preset-stage-2": "6.18.0",
     "chai": "3.5.0",
     "codecov.io": "0.1.6",
     "eslint": "3.12.2",