Fix typo in bin/check-merged.sh

Change-Id: I7ca06602179e35d5ce86879b1081299a841feba9
Reviewed-on: https://gerrit.libreoffice.org/12431
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>