Merge pull request #20 from NodeOS/greenkeeper-async-2.1.4

async@2.1.4 breaks build 🚨

Author: piranna

package.json

@@ -49,7 +49,7 @@
   "author": "Jesús Leganés Combarro 'piranna' <piranna@gmail.com>",
   "license": "MIT",
   "dependencies": {
-    "async": "^2.1.2",
+    "async": "^2.1.4",
     "download-manager": "^0.1.3",
     "fs-extra": "^1.0.0",
     "prebuild-install": "2.1.0"