Update chai to the latest version 🚀 (#30)

* chore(package): update chai to version 4.0.2

* Update package.json

Author: greenkeeper[bot]

package.json

@@ -24,7 +24,7 @@
   },
   "devDependencies": {
     "mocha": "3.x.x",
-    "chai": "3.x.x",
+    "chai": "4.x.x",
     "pre-commit": "1.x.x"
   }
 }