get rubygems' submodules else source builds fail
get rubygems' submodules else source builds fail

rubygems/rubygems started vendoring bundler as a submodule[1]
in 2016. Possibly we don't have any projects using RubyGems from
a git reference since then. But in trying to do so, builds of rubygems
from a get ref error out with:

    ERROR:  While executing gem ... (Errno::ENOENT)
    No such file or directory @ dir_chdir - bundler/lib

So, as much as submodules sadden me, to run rubygems' setup.rb,
we need to initialize and update the repo's submodules.

[1] https://github.com/rubygems/rubygems/commit/aa83d3799579b8714b1f9c8c78afdb4e176bba58#diff-db852b71825b722d7e0dcb631d77414d

Signed-off-by: Robb Kidd <a629c362624370ec351e141df0bd1d27621ff790@thekidds.org>

aerobase/omnibus-software,chef/omnibus-software,aerobase/omnibus-software,higanworks/omnibus-software,chef/omnibus-software,mattray/omnibus-software,aerobase/omnibus-software,aerobase/omnibus-software,mattray/omnibus-software,mattray/omnibus-software,chef/omnibus-software,higanworks/omnibus-software,chef/omnibus-software,chef/omnibus-software,higanworks/omnibus-software,mattray/omnibus-software,chef/omnibus-software,higanworks/omnibus-software,mattray/omnibus-software,aerobase/omnibus-software