Fix block and proc definition to work with Ruby 3.0

[JHK]

This should fix the following warning in Ruby 2.7, which will become breaking in 3.0:

/var/lib/gems/2.7.0/gems/arachnid2-0.4.0/lib/arachnid2/typhoeus.rb:27: warning: Capturing the given block using Proc.new is deprecated; use `&block` instead