Resize advanced search filters to allow more space by default

Resize advanced search filters to allow more space by default

By default, the space allotted was perfect at 800px which worked in
Chrome browser just fine.  But viewing in Firefox rendered the elements
slightly larger and wrapped some filters instead of displaying four
in a row as expected.

Increase the adv_search_filters from 800px to 850px to allow for more
space.

Signed-off-by: Ben Shum <bshum@biblio.org>
Signed-off-by: Lebbeous Fogle-Weekley <lebbeous@esilibrary.com>
Signed-off-by: Dan Wells <dbw2@calvin.edu>