`click.BaseCommand` deprecation warning

[michellewang]

With the latest click version (8.3.0 at the time of writing) we get a DeprecationWarning at trogon/trogon/introspect.py:8:

DeprecationWarning: 'BaseCommand' is deprecated and will be removed in Click 9.0. Use 'Command' instead.
    from click import BaseCommand, ParamType

To reproduce: run the tests.

I think this should be a straightforward replacement unless I am missing anything.