Changed mocha to mocha --exit

When using `chai-http`, `mocha` doesn't seem to exit but instead waits.

There seems to be some workarounds (chaijs/chai-http#178), but adding this argument is the easiest for now until more code is written.

package.json

@@ -4,7 +4,7 @@
   "description": "A NuGet server written in Node. Designed to host a Chocolatey internal package feed.",
   "main": "index.js",
   "scripts": {
-    "test": "mocha"
+    "test": "mocha --exit"
   },
   "husky": {
     "hooks": {