Update dependency chai to v4

Author: renovate-bot

package.json

@@ -34,7 +34,7 @@
 		"babel-eslint": "7.2.3",
 		"babel-preset-es2015": "6.24.1",
 		"babel-register": "6.26.0",
-		"chai": "3.5.0",
+		"chai": "4.2.0",
 		"eslint": "3.19.0",
 		"eslint-plugin-babel": "3.3.0",
 		"mocha": "3.5.3",