chore(package): update chai to version 4.1.0 (#117)

Author: greenkeeper[bot]

package.json

@@ -18,7 +18,7 @@
     "babel-core": "^6.24.0",
     "babel-preset-es2015": "^6.18.0",
     "babel-register": "^6.24.0",
-    "chai": "^3.5.0",
+    "chai": "^4.1.0",
     "coveralls": "^2.11.16",
     "cross-env": "^3.1.4",
     "mocha": "^3.2.0",