Bug 20122: Explicitly set path to fix emptying cart functionality

Bug 20122: Explicitly set path to fix emptying cart functionality

This is caused by bib_list not being deleted.
The path was not explicitly set.
This patch adds path=/ explicitly to ensure it
does get deleted.

TEST PLAN
---------
1) search for 'the' in OPAC
2) add several items to cart.
3) look at your cart.
4) empty and close the cart, select all->remove
   -- either way window closes and it looks empty.
5) refresh the page
   -- cart comes back.
   -- in chromium inspecting the page, specifically
      the "Application" area, bib_list is shown as
      a cookie still.
6) apply patch
7) restart_all and empty cache forcing JS reload
8) repeat steps 1-5
   -- this time cart stays empty.
   -- and the bib_list cookie is gone

Signed-off-by: Roch D'Amour <roch.damour@inlibro.com> using firefox 59.0.2
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>