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

https://greenkeeper.io/

Author: greenkeeperio-bot

package.json

@@ -61,7 +61,7 @@
     "babel-core": "6.17.0",
     "babel-plugin-add-module-exports": "0.2.1",
     "babel-preset-es2015": "6.16.0",
-    "babel-preset-stage-2": "6.17.0",
+    "babel-preset-stage-2": "6.18.0",
     "chai": "^3.4.1",
     "commitizen": "^2.8.2",
     "coveralls": "^2.11.6",