List the installed versions of ruby

    CLI Example:

    .. code-block:: bash

        salt '*' rbenv.versions

def versions(runas=None):
    '''
    List the installed versions of ruby

    CLI Example:

    .. code-block:: bash

        salt '*' rbenv.versions
    '''
    ret = _rbenv_exec(['versions', '--bare'], runas=runas)
    return [] if ret is False else ret.splitlines()