Merge pull request #41 from testingbot/greenkeeper/async-3.1.1

fix(package): update async to version 3.1.1

Author: jochen-testingbot

package.json

@@ -10,7 +10,7 @@
     "build": "babel lib -d build"
   },
   "dependencies": {
-    "async": "^2.1.4"
+    "async": "^3.1.1"
   },
   "devDependencies": {
     "babel-cli": "^6.0.0",