fix(cli): enforce subcommand as required

without enforcing subcommand, exception would be raised when running `cz -n test` or `cz --debug`

Author: Lee-W

commitizen/cli.py

@@ -23,6 +23,7 @@
     ],
     "subcommands": {
         "title": "commands",
+        "required": True,
         "commands": [
             {
                 "name": "ls",