Bug 18848: borrowers.lastseen comment typo

Bug 18848: borrowers.lastseen comment typo

Typo in comment for the lastseen column in the borrowers table.

To test:
1. Verify lastseen column displays "last time a patron has been seed"
2. Apply patch
3. Verify lastseen column changed to "last time a patron has been seen"

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
(cherry picked from commit 23b84c0b6532d9c42894b648891d835e7624db49)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>