chore(package): update mocha to version 4.0.0 (#22)

package.json

@@ -42,7 +42,7 @@
   "devDependencies": {
     "assume": "~1.5.0",
     "istanbul": "~0.4.5",
-    "mocha": "~3.5.0",
+    "mocha": "~4.0.0",
     "pre-commit": "~1.2.0",
     "request": "~2.83.0"
   }