Pass rubygems_version to 'rvm install'

See: https://github.com/wayneeseguin/rvm-gem/pull/14

This pull request paired with the above makes it so a specified :rubygems_version for a rvm_ruby is used to install that ruby. Locking in an rvm version with ```node[:rvm][:version]``` will otherwise result in eventual convergence errors during ruby installs due to missing rubygem archive checksums.

e.g. the following error showed with rvm version 1.22.13 and ruby-1.8.7-p374:

>
> There is no checksum for 'http://production.cf.rubygems.org/rubygems/rubygems-2.0.14.tgz' or 'rubygems-2.0.14.tgz', it's not possible to validate it.
This could be because your RVM install's list of versions is out of date. You may want to
update your list of rubies by running 'rvm get stable' and try again.
If that does not resolve the issue and you wish to continue with unverified download
add '--verify-downloads 1' after the command.
> 
> There has been an error while trying to fetch rubygems. 
> Halting the installation.

With the patches, using something like the following will work now and 6 months from now:

    node.default[:rvm][:version] = '1.22.13'
    ….
    node.default['rvm']['rubies'] << {
      'version' =>'ruby-1.8.7-p374',
      'rubygems_version' => '1.8.23'
    }