fix(package): update async to version 3.1.1

Closes #42

Author: greenkeeper[bot]

package.json

@@ -32,7 +32,7 @@
     },
     "homepage": "https://github.com/nodefluent/kafka-connect#readme",
     "dependencies": {
-        "async": "~2.6.2",
+        "async": "~3.1.1",
         "bluebird": "~3.5.4",
         "body-parser": "~1.19.0",
         "debug": "~4.1.1",