chore(package): update commitizen to version 4.0.2

Closes #7

Author: greenkeeper[bot]

package.json

@@ -63,7 +63,7 @@
     "@semantic-release/github": "^5.2.10",
     "@semantic-release/npm": "^5.1.4",
     "@semantic-release/release-notes-generator": "^7.1.4",
-    "commitizen": "^3.1.1",
+    "commitizen": "^4.0.2",
     "coveralls": "^3.0.3",
     "cz-conventional-changelog": "^2.1.0",
     "del": "^4.1.0",