chore(package): update mocha to version 6.1.3

Closes #6

Author: greenkeeper[bot]

package.json

@@ -25,7 +25,7 @@
   },
   "devDependencies": {
     "chai": "^4.1.2",
-    "mocha": "^4.0.0",
+    "mocha": "^6.1.3",
     "standard": "^10.0.3"
   }
 }