chore(package): update mocha to version 6.1.4

Closes #1237

Author: greenkeeper[bot]

package.json

@@ -50,6 +50,6 @@
     "karma-firefox-launcher": "^1.0.0",
     "karma-mocha": "^1.0.1",
     "karma-sauce-launcher": "^1.2.0",
-    "mocha": "^5.0.0"
+    "mocha": "^6.1.4"
   }
 }