chore(package): update mocha to version 6.2.1

Closes #23

Author: greenkeeper[bot]

package.json

@@ -21,7 +21,7 @@
   },
   "devDependencies": {
     "redis": "~2.8.0",
-    "mocha": "~5.2.0",
+    "mocha": "~6.2.1",
     "chai": "~4.2.0",
     "sinon": "~7.1.1",
     "sinon-chai": "~3.3.0",