chore(package): update chai to version 4.0.1 (#46)

Author: greenkeeper[bot]

package.json

@@ -27,7 +27,7 @@
   },
   "homepage": "https://github.com/yargs/y18n",
   "devDependencies": {
-    "chai": "^3.4.1",
+    "chai": "^4.0.1",
     "coveralls": "^2.11.6",
     "mocha": "^3.0.0",
     "nyc": "^11.0.1",