chore(package): update commitizen to version 4.0.0

Closes #22

Author: greenkeeper[bot]

package.json

@@ -40,7 +40,7 @@
     "all-contributors-cli": "^4.6.0",
     "babel-eslint": "^8.2.3",
     "babel-jest": "23.0.1",
-    "commitizen": "^2.9.6",
+    "commitizen": "^4.0.0",
     "eslint": "^4.6.1",
     "eslint-config-airbnb-base": "^12.1.0",
     "eslint-config-prettier": "^2.4.0",