chore(package): update mocha to version 6.1.0

Closes #24

Author: greenkeeper[bot]

package.json

@@ -32,7 +32,7 @@
   },
   "devDependencies": {
     "coveralls": "^3.0.0",
-    "mocha": "^5.0.0",
+    "mocha": "^6.1.0",
     "nock": "^10.0.0",
     "nyc": "^12.0.1",
     "should": "^13.1.3"