chore(package): update chai to version 4.1.1

Closes #25

Author: greenkeeper[bot]

package.json

@@ -60,7 +60,7 @@
     "babel-preset-stage-1": "^6.24.1",
     "babel-register": "^6.24.1",
     "babel-runtime": "^6.23.0",
-    "chai": "^3.5.0",
+    "chai": "^4.1.1",
     "copy": "^0.3.0",
     "coveralls": "^2.13.0",
     "eslint": "^3.19.0",