chore(package): update chai to version 4.1.0

Closes #10

Author: greenkeeper[bot]

package.json

@@ -17,7 +17,7 @@
     "ws": "^2.3.1"
   },
   "devDependencies": {
-    "chai": "^3.5.0",
+    "chai": "^4.1.0",
     "coffee-script": "^1.12.5",
     "fbp": "^1.5.0",
     "mocha": "^3.2.0",