chore(package): update mocha to version 5.0.3

Closes #6

package.json

@@ -25,7 +25,7 @@
   "devDependencies": {
     "assume": "~1.5.0",
     "istanbul": "~0.4.5",
-    "mocha": "~3.2.0",
+    "mocha": "~5.0.3",
     "pagelet": "~0.9.0",
     "pre-commit": "~1.2.0"
   }