chore(package): update babel-preset-es2015 to version 6.24.1

Closes #33

https://greenkeeper.io/

Author: greenkeeper[bot]

package.json

@@ -56,7 +56,7 @@
     "babel-loader": "6.2.8",
     "babel-plugin-external-helpers": "6.18.0",
     "babel-polyfill": "6.16.0",
-    "babel-preset-es2015": "6.18.0",
+    "babel-preset-es2015": "6.24.1",
     "babel-preset-stage-0": "6.16.0",
     "chai": "3.5.0",
     "coveralls": "2.11.15",