Sphinx is currently issuing the following warnings for projects using
this extension.
RemovedInSphinx30Warning: sphinx.locale.l_() is deprecated. Please
use `_()` instead.
Head this off before it becomes an issue.
Change-Id: I108d36ab909a7afd4fd28bfb565812f69ae02118
Signed-off-by: Stephen Finucane <stephenfin@redhat.com>