config.gemspec: use `funding_url` rather than `post_install_message`

[pda]

Hello 👋🏼

This is a friendly PR to shift the request for funding from the general-purpose post_install_message to the specific funding_uri system supported by bundler 2.2+.

I think this is more in line with etiquette of the community. To quantify that with some anecdata, the main Rails app I work on has ~340 gem dependencies, and I took the time to do a clean install and observe the post_install_messages. There's 8 in total:

• 4 API change/deprecation notice
• 1 notice of a non-declared soft dependency on another gem
• 1 notice regarding EOL/maintenance schedule
• 1 nonsense from httparty
• 1 relating to sponsorship/funding: config

Related:

If you develop a gem that needs funding, make sure you fill in the funding_uri metadata in your gemspec, like this … … bundle fund will start reporting all of your dependencies that need funding.

— https://bundler.io/blog/2020/12/09/bundler-v2-2.html

"funding_uri" => "https://example.com/donate"

— https://guides.rubygems.org/specification-reference/

Thanks! 🙏🏼

[pkuczynski]

Yeah, make sense @pda, thanks!

[pkuczynski]

Released as 5.5.0

[pda]

Thanks very much @pkuczynski 🙏🏼