resolv.rb: workaround for recent Rubygems

* lib/resolv.rb (Resolv::Hosts): get rid of load error in require
  which causes recent Rubygems to build all extension libraries.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43355 b2dd03c8-39d4-4d8f-98ff-823fe69b080e