require stringio before use

[wizardofelves]

Hello!

I upgraded to Ruby 3.1, and when I did i started receiving errors that uninitialized constant StringIO (NameError). I feel this is similar to the PR for require delegate that had been addressed earlier.

https://github.com/mileszs/wicked_pdf/pull/1019/files

When running WickedPDF via the ruby command using ruby 3.1, I received

/usr/local/rvm/rubies/ruby-3.1.3/lib/ruby/3.1.0/delegate.rb:61:in `const_get': uninitialized constant StringIO (NameError)

when running the following command

"bundle exec ruby -e 'require \"wicked_pdf\"; WickedPdf.new.pdf_from_string(\"<p>Ya did it</p>\"); puts \"great!"'"

In all examples I've seen this used, we should first require this.

https://ruby-doc.org/stdlib-2.5.1/libdoc/stringio/rdoc/StringIO.html

Thank you

[unixmonkey]

Thanks!