Update Travis CI to latest OTP19.1
Update Travis CI to latest OTP19.1

benoitc/rebar3,vladdu/rebar3,benoitc/rebar3,ferd/rebar3,tsloughter/rebar3,djnym/rebar3,rebar/rebar3,lrascao/rebar3,rebar/rebar3,saleyn/rebar3,erlang/rebar3