fix(package): update async to version 3.1.0

Closes #107

Author: greenkeeper[bot]

package.json

@@ -16,7 +16,7 @@
     "url": "https://github.com/leecade/fe/issues"
   },
   "dependencies": {
-    "async": "^2.1.2",
+    "async": "^3.1.0",
     "autoprefixer": "^6.5.1",
     "babel-core": "^6.18.2",
     "babel-loader": "^6.2.7",