chore(package): update mocha to version 6.2.2

Closes #12

Author: greenkeeper[bot]

package.json

@@ -13,7 +13,7 @@
   "devDependencies": {
     "chai": "^4.0.2",
     "coffee-script": "^1.9.0",
-    "mocha": "^5.0.0",
+    "mocha": "^6.2.2",
     "mocha-gwt": "^0.2.0",
     "pikaday": "^1.7.0",
     "ramda": "^0.25.0",