back to travis for ci for now
back to travis for ci for now

Replacing README build status icon with travis until drone.io support PR builds.
syl20bnr/relx,Licenser/relx,zugolosian/relx,umatomba/relx,RJ/relx,tsloughter/relx,bitwalker/relx,erlware/relx,lrascao/relx,ingwinlu/relx,timclassic/relx,bsmr-erlang/relx,priestjim/relx,ethercrow/relx