FIX: Wrong extension in docsite file

[AngelGuerra]

Hello folks! I have seen that there is a problem in one of the links in the documentation:

If you navigate to https://dry-rb.org/gems/dry-cli/main/ and click in the menu on Commands with subcommands and params, it will result in downloading a file instead of navigating. I suspect it is because the file extension is .md instead of .html.md, this PR fixes that error.

Thanks for your work!

How to reproduce

• Go to https://dry-rb.org/gems/dry-cli/main/.
• Click on Commands with subcommands and params.

Or...

• Go to https://dry-rb.org/gems/dry-cli/main/commands-with-subcommands-and-params.