chore(package): update chai to version 4.1.1

Closes #28

Author: greenkeeper[bot]

package.json

@@ -27,7 +27,7 @@
   },
   "dependencies": {},
   "devDependencies": {
-    "chai": "^3.5.0",
+    "chai": "^4.1.1",
     "eslint": "^3.12.2",
     "eslint-config-fullstack": "^3.0.0",
     "eslint-plugin-react": "^7.0.0",