Changed incorrect ResolverFailure -> ResolutionFailure (fixes socketry#9)

Author: ioquatix

lib/rubydns/transaction.rb

@@ -124,7 +124,7 @@ def passthrough(resolver, options = {}, &block)
 case response
 when RubyDNS::Message
 yield response
-when RubyDNS::ResolverFailure
+when RubyDNS::ResolutionFailure
 failure!(:ServFail)
 else
 # This shouldn't ever happen, but if it does for some reason we shouldn't hang.