travis: get compatible version of rubygems-update
travis: get compatible version of rubygems-update

toy/image_optim,mihailim/image_optim,ramiroaraujo/image_optim,mihailim/image_optim,toy/image_optim,mihailim/image_optim,toy/image_optim,ramiroaraujo/image_optim,ramiroaraujo/image_optim