Bug 18804: (bug 16286 follow-up) Update the "save category" elt selector

Bug 18804: (bug 16286 follow-up) Update the "save category" elt selector

Bug 16286 replaced the submit node:
  <input type="button" value="Save" onclick="Check(this.form);" />
with
  <input type="submit" value="Save" />

Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>
Signed-off-by: Lee Jamison <ldjamison@marywood.edu>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
(cherry picked from commit a88f540ec1a0f7e1f876f3811d0e44cb3ff3a612)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>