Remove redundant `dup`
Remove redundant `dup`

Hash#merge returns a new Hash:
http://ruby-doc.org/core-2.0.0/Hash.html#method-i-merge
lstoll/httpserious,rayzhng/httparty,sferik/httparty,landonwilkins/httparty,eibay/httparty,rayzhng/httparty,charliesome/httpserious,MichaelWiss/httparty,kristjan/httsoiree,jordanpagewhite/httparty,sideci-sample/sideci-sample-httparty,eibay/httparty,jordanpagewhite/httparty,jnunemaker/httparty,killerwails/httparty,killerwails/httparty,jordanpagewhite/httparty,RobinsonKameron/httparty,lstoll/httpserious,jpb/httparty,ffleming/httparty,tokafish/httparty,wakermahmud/httparty,bob-frost/httparty,MichaelWiss/httparty,supremebeing7/httparty,sideci-sample/sideci-sample-httparty,wakermahmud/httparty,dpatlut/httparty,jpb/httparty,bob-frost/httparty,kristjan/httsoiree,eibay/httparty,jpb/httparty,tokafish/httparty,jnunemaker/httparty,supremebeing7/httparty,dpatlut/httparty,rayzhng/httparty,charliesome/httpserious,landonwilkins/httparty,RobinsonKameron/httparty,MichaelWiss/httparty,jnunemaker/httparty,supremebeing7/httparty,bob-frost/httparty,kristjan/httsoiree,tokafish/httparty,wakermahmud/httparty,landonwilkins/httparty,dpatlut/httparty,lstoll/httpserious,jayjlawrence/httparty,ffleming/httparty,ffleming/httparty,RobinsonKameron/httparty,jayjlawrence/httparty,sferik/httparty,killerwails/httparty,charliesome/httpserious,jayjlawrence/httparty