chore(package): update mocha to version 6.2.1

Closes #39

Author: greenkeeper[bot]

package.json

@@ -42,7 +42,7 @@
     "chai": "4.1.2",
     "coveralls": "2.13.2",
     "global": "4.3.2",
-    "mocha": "3.5.1",
+    "mocha": "6.2.1",
     "husky": "0.13.4",
     "rimraf": "2.6.2",
     "npm-run-all": "4.1.0"