Bug 11308: fix RSS page in bootstrap theme

Bug 11308: fix RSS page in bootstrap theme

To test:
1/ Do a search in the opac, click on the rss feed icon
2/ Notice the page renders, not like an rss feed should
3/ Apply the patch and refresh
4/ Page should now be (more) valid xml

Signed-off-by: Mark Tompsett <mtompset@hotmail.com>
Signed-off-by: Katrin Fischer <Katrin.Fischer.83@web.de>
Small change, big difference. With the patch the content of
the RSS feed renders like it does for the prog theme.

Signed-off-by: Galen Charlton <gmc@esilibrary.com>
(cherry picked from commit 71a3516d211600d35e4ddeef45f5403affc09598)
Signed-off-by: Fridolin SOMERS <fridolin.somers@biblibre.com>