Add {cli} to maptiler_sytle() so that the link is properly formatted

[benjaminhlina]

Fixes issue #219

[walkerke]

Thanks so much for catching this, @benjaminhlina! I'd rather not add {cli} as a hard dependency for one message, so I fixed it by rewording the message so the URL isn't followed by a comma. That'll be on main shortly. Closing this in favor of that fix, but I really appreciate the report and the PR.

[benjaminhlina]

Yeah totally understandable as it's unnecessary for a single message. Is there a specific reason why you've chosen {rlang} over {cli} for messages and errors? This is out curiosity, as I often gravitate towards {cli} but wonder if there's advantages that {rlang} provides.