chore(package): update chai to version 4.0.0

Author: greenkeeper[bot]

package.json

@@ -22,7 +22,7 @@
   },
   "devDependencies": {
     "amqplib": "^0.5.1",
-    "chai": "~3.5.0",
+    "chai": "~4.0.0",
     "grunt": "~1.0.1",
     "coffee-script": "^1.8.0",
     "grunt-coffeelint": "~0.0.6",