chore(package): update mocha to version 6.2.0

Closes #9

Author: greenkeeper[bot]

package.json

@@ -42,7 +42,7 @@
   "devDependencies": {
     "assume": "~2.1.0",
     "istanbul": "~0.4.5",
-    "mocha": "~3.5.0",
+    "mocha": "~6.2.0",
     "pre-commit": "~1.2.0",
     "url-parse": "~1.4.0"
   }