chore(package): update mocha to version 6.1.1

Closes #3

Author: greenkeeper[bot]

package.json

@@ -24,7 +24,7 @@
     "dotenv": "^4.0.0",
     "eslint": "^4.8.0",
     "eslint-config-google": "^0.9.1",
-    "mocha": "^4.0.1",
+    "mocha": "^6.1.1",
     "nyc": "^11.2.1"
   },
   "dependencies": {