chore(package): update mocha to version 6.1.0

Closes #15

Author: greenkeeper[bot]

package.json

@@ -30,6 +30,6 @@
     "chai-as-promised": "^6.0.0",
     "eslint": "^4.1.0",
     "istanbul": "^1.0.0-alpha.2",
-    "mocha": "^3.0.1"
+    "mocha": "^6.1.0"
   }
 }