Update server_zmq.rb
Update server_zmq.rb

I feel almost stupid to send in a pull request for this: There is a typo in line 88: "rZMQ::Util.error_string" instead of "ZMQ::Util.error_string".
srizzling/log-courier,MichaelLiZhou/log-courier,dixitk13/log-courier,dixitk13/log-courier,linearregression/log-courier,linearregression/log-courier,linearregression/log-courier,srizzling/log-courier,MichaelLiZhou/log-courier,scrapinghub/log-courier,scrapinghub/log-courier,scrapinghub/log-courier,dixitk13/log-courier,srizzling/log-courier,MichaelLiZhou/log-courier