Issue certificates to all students who earn them, even if they are in an audit track

LMS-2573

lms/templates/dashboard/_dashboard_certificate_information.html

@@ -49,7 +49,7 @@ else:
     % if cert_status['show_disabled_download_button']:
       <li class="action"><span class="disabled">
           ${_("Your {cert_name_short} is Generating").format(cert_name_short=cert_name_short)}</span></li>
-    % elif cert_status['show_download_url'] and enrollment.mode == 'honor':
+    % elif cert_status['show_download_url'] and (enrollment.mode == 'honor' or enrollment.mode == 'audit'):
       <li class="action action-certificate">
       <a class="btn" href="${cert_status['download_url']}"
          title="${_('This link will open/download a PDF document')}">