/usr/bin/ruby is not available. But they can take the desired
ruby binary from the RUBY environment variable. Since we can not
really set that properly via pre_install, set it within the loop
to the current ruby binary before calling the ruby part of
gem_install.sh.
OBS-URL: https://build.opensuse.org/package/show/devel:languages:ruby/ruby-common?expand=0&rev=147
