update travis yml
update travis yml

there is some problem with node on travis server.
node doesn't required to build docker image anyway.

lteacher/codewars-runner-cli,Codewars/codewars-runner,OverZealous/codewars-runner-cli,Codewars/codewars-runner-cli,lteacher/codewars-runner-cli,Codewars/codewars-runner,Codewars/codewars-runner,OverZealous/codewars-runner-cli,OverZealous/codewars-runner-cli,lteacher/codewars-runner-cli,DonaldKellett/codewars-runner-cli,DonaldKellett/codewars-runner-cli,Codewars/codewars-runner-cli,Codewars/codewars-runner-cli,OverZealous/codewars-runner-cli,OverZealous/codewars-runner-cli,OverZealous/codewars-runner-cli,Codewars/codewars-runner-cli,Codewars/codewars-runner-cli,lteacher/codewars-runner-cli,Codewars/codewars-runner,DonaldKellett/codewars-runner-cli,DonaldKellett/codewars-runner-cli,DonaldKellett/codewars-runner-cli,DonaldKellett/codewars-runner-cli,lteacher/codewars-runner-cli,Codewars/codewars-runner-cli,lteacher/codewars-runner-cli,Codewars/codewars-runner-cli,lteacher/codewars-runner-cli,lteacher/codewars-runner-cli,OverZealous/codewars-runner-cli,lteacher/codewars-runner-cli,OverZealous/codewars-runner-cli,Codewars/codewars-runner-cli,Codewars/codewars-runner-cli,Codewars/codewars-runner-cli,Codewars/codewars-runner-cli,OverZealous/codewars-runner-cli,Codewars/codewars-runner-cli,lteacher/codewars-runner-cli,DonaldKellett/codewars-runner-cli,DonaldKellett/codewars-runner-cli,OverZealous/codewars-runner-cli,OverZealous/codewars-runner-cli,Codewars/codewars-runner,DonaldKellett/codewars-runner-cli,OverZealous/codewars-runner-cli,lteacher/codewars-runner-cli,DonaldKellett/codewars-runner-cli,Codewars/codewars-runner-cli,OverZealous/codewars-runner-cli,DonaldKellett/codewars-runner-cli,OverZealous/codewars-runner-cli,Codewars/codewars-runner-cli