chore(package): update chai to version 4.0.1

Author: greenkeeper[bot]

package.json

@@ -37,7 +37,7 @@
     "babel-plugin-istanbul": "^4.0.0",
     "babel-preset-es2015": "^6.6.0",
     "babel-register": "^6.11.5",
-    "chai": "^3.5.0",
+    "chai": "^4.0.1",
     "chokidar-cli": "^1.2.0",
     "coveralls": "^2.11.9",
     "eslint": "^3.0.0",