chore(package): update mocha to version 6.1.0

Closes #10

Author: greenkeeper[bot]

package.json

@@ -7,7 +7,7 @@
     "jsdom": "9.12.0",
     "jsdom-global": "2.1.1",
     "jslint": "0.10.3",
-    "mocha": "3.4.2"
+    "mocha": "6.1.0"
   },
   "scripts": {
     "test": "jslint de-pre.js && mocha test/**/*.js -r jsdom-global/register"