chore(package): update chai to version 4.1.1

Closes #47

Author: greenkeeper[bot]

package.json

@@ -58,7 +58,7 @@
     "babel-polyfill": "6.16.0",
     "babel-preset-es2015": "6.18.0",
     "babel-preset-stage-0": "6.16.0",
-    "chai": "3.5.0",
+    "chai": "4.1.1",
     "coveralls": "2.11.15",
     "documentation": "4.0.0-beta15",
     "eslint": "3.9.1",