chore(package): update chai to version 4.1.2

Closes #68

Author: greenkeeper[bot]

package.json

@@ -62,7 +62,7 @@
     "babel-plugin-istanbul": "3.1.2",
     "babel-plugin-transform-es2015-modules-umd": "6.18.0",
     "babel-preset-es2015": "6.18.0",
-    "chai": "3.5.0",
+    "chai": "4.1.2",
     "coveralls": "2.11.15",
     "documentation": "4.0.0-beta16",
     "eslint": "3.12.2",