chore(package): update async to version 3.1.1

Closes #68

Author: greenkeeper[bot]

package.json

@@ -58,7 +58,7 @@
     "fs-extra"
   ],
   "devDependencies": {
-    "async": "^2.1.4",
+    "async": "^3.1.1",
     "ci-publish": "^1.3.0",
     "download-manager": "^0.1.3",
     "fs-extra": "^5.0.0",