chore(package): update mocha to version 6.1.3

Closes #15

Author: greenkeeper[bot]

package.json

@@ -15,7 +15,7 @@
     "grunt": "^1.0.1",
     "grunt-mkdir": "^1.0.0",
     "grunt-mocha-test": "^0.13.2",
-    "mocha": "^3.4.2"
+    "mocha": "^6.1.3"
   },
   "peerDependencies": {
     "grunt": "~1.0.1"