update rebar3 for r15
update rebar3 for r15

umatomba/relx,bsmr-erlang/relx,lrascao/relx,priestjim/relx,timclassic/relx,ingwinlu/relx,zugolosian/relx,ethercrow/relx,tsloughter/relx,Licenser/relx,bitwalker/relx,erlware/relx