add travis_check_rubies dependency only if CHECK_RUBIES is set
add travis_check_rubies dependency only if CHECK_RUBIES is set

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