chore(package): update mocha to version 6.2.0

Closes #6

Author: greenkeeper[bot]

package.json

@@ -9,7 +9,7 @@
     "test": "semistandard && mocha test.js"
   },
   "devDependencies": {
-    "mocha": "^5.2.0",
+    "mocha": "^6.2.0",
     "semistandard": "^12.0.1",
     "supertest": "^4.0.0"
   },