replace call to flatten_once with flatten(1)
replace call to flatten_once with flatten(1)

according to the comment at https://github.com/travis-ci/travis-support/blob/master/lib/core_ext/array/flatten_once.rb#L3

Tiger66639/travis-core,final-ci/travis-core,kidaa/travis-core,developerfm/travis-core,kidaa/travis-core,Tiger66639/travis-core,travis-ci/travis-core,developerfm/travis-core,final-ci/travis-core,GistIcon/travis-core,travis-repos/travis-core,developerfm/travis-core,final-ci/travis-core,kidaa/travis-core,travis-ci/travis-core,Tiger66639/travis-core,GistIcon/travis-core,jantman/travis-core,travis-repos/travis-core,travis-ci/travis-core,jantman/travis-core,GistIcon/travis-core