Add --exit flag to mocha command line to force exit.

Since v4 mocha doesn't force-exit if a process or a socket is still running.

mochajs/mocha#3044

package.json

@@ -6,7 +6,7 @@
   "scripts": {
     "build": "node node_modules/grunt/bin/grunt",
     "start": "node src/server.js",
-    "test": "mocha test/**/*.test.js",
+    "test": "mocha --exit test/**/*.test.js",
     "release": "true"
   },
   "repository": {