chore(package): update commitizen to version 4.0.0

Closes #25

Author: greenkeeper[bot]

package.json

@@ -94,7 +94,7 @@
     "@types/node": "^9.3.0",
     "all-contributors-cli": "^4.10.1",
     "colors": "^1.1.2",
-    "commitizen": "^2.9.6",
+    "commitizen": "^4.0.0",
     "coveralls": "^3.0.0",
     "cross-env": "^5.0.1",
     "cz-conventional-changelog": "^2.0.0",