chore(package): update mocha to version 6.1.0

Closes #21

Author: greenkeeper[bot]

package.json

@@ -65,7 +65,7 @@
     "eslint-plugin-node": "^8.0.0",
     "eslint-plugin-standard": "^4.0.0",
     "istanbul": "^1.1.0-alpha.1",
-    "mocha": "^5.0.0",
+    "mocha": "^6.1.0",
     "semistandard": "^13.0.0"
   }
 }