chore(package): update commitizen to version 4.0.0

Author: greenkeeper[bot]

package.json

@@ -39,7 +39,7 @@
  "ava": "^2.0.0",
  "clear-module": "^3.0.0",
  "codecov": "^3.0.0",
- "commitizen": "^3.0.0",
+ "commitizen": "^4.0.0",
  "cz-conventional-changelog": "^2.0.0",
  "file-url": "^3.0.0",
  "get-stream": "^5.0.0",