url_encode: use CGI.escapeURIComponent

[byroot]

Ref: ruby/cgi#26

This native implementation is much faster and available in cgi 0.3.3.

[byroot]

I'm not too sure why 2.5 CI is failing, it's like it's not loading cgi as a gem but using the stdlib version?

I can add a conditional to handle this case. Let me know what you think @k0kubun.

[k0kubun]

it's like it's not loading cgi as a gem but using the stdlib version?

stdlib could be updated only if the Ruby version has it as a default gem instead of a non-gem standard library. CGI has been promoted to a default gem on 2.7 https://github.com/ruby/ruby/blob/v2_7_0/NEWS. Looks like 2.6 is not tested in the workflow (a separate problem), but it wouldn't work in Ruby 2.6 either.

Given that Ruby 2.6 is EOL, I'm okay with requiring Ruby 2.7+ from the next ERB version. Can you do it in this PR to fix the CI?

[byroot]

Done.