travis: drop go 1.3, add 1.6
travis: drop go 1.3, add 1.6

3ofcoins/appc-spec,appc/spec,squeed/spec,3ofcoins/appc-spec,dgonyeo/spec,jonboulle/spec,3ofcoins/appc-spec,appc/spec,jonboulle/spec,dgonyeo/spec,appc/spec,jonboulle/spec,squeed/spec,squeed/spec,dgonyeo/spec