chore(package): update chai to version 4.1.2

Closes #16

Author: greenkeeper[bot]

package.json

@@ -14,7 +14,7 @@
   "dependencies": {},
   "devDependencies": {
     "amqplib": "^0.5.1",
-    "chai": "~3.5.0",
+    "chai": "~4.1.2",
     "coffee-script": "^1.8.0",
     "mocha": "~3.4.2",
     "msgflo": "^0.10.0",