chore(package): update mocha to version 6.0.1

Closes #7

Author: greenkeeper[bot]

package.json

@@ -15,7 +15,7 @@
   "devDependencies": {
     "expect.js": "^0.3.1",
     "jshint": "^2.8.0",
-    "mocha": "^4.0.1"
+    "mocha": "^6.0.1"
   },
   "optionalDependencies": {},
   "bugs": {