chore(package): update commitizen to version 3.1.2

Closes #18

Author: greenkeeper[bot]

package.json

@@ -31,7 +31,7 @@
     "@semantic-release/git": "^4.0.1",
     "@semantic-release/github": "^4.0.0",
     "@semantic-release/npm": "^3.0.0",
-    "commitizen": "^2.9.6",
+    "commitizen": "^3.1.2",
     "cz-conventional-changelog": "^2.1.0",
     "husky": "^0.14.3",
     "semantic-release": "^15.0.2",