chore(package): update mocha to version 6.0.2

Closes #4

Author: greenkeeper[bot]

package.json

@@ -17,7 +17,7 @@
   "devDependencies": {
     "codacy-coverage": "^2.0.1",
     "istanbul": "^0.4.5",
-    "mocha": "^4.0.0",
+    "mocha": "^6.0.2",
     "standard": "^10.0.0"
   },
   "repository": {