fix logerrit on mac

where my initial commit seems not to have done the job.

Change-Id: I437df21fc5164eace48c8a2dc093e2c3dcc37826
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/113661
Tested-by: Jenkins
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>

logerrit

@@ -26,7 +26,7 @@ submit() {
         if [ "$BRANCH" = "master" ]; then
             WEEKOLDDATE=$(date --date="7 days ago" +%s 2> /dev/null)
             if [ "$WEEKOLDDATE" = "" ]; then
-                WEEKOLDDATE=$(date -v7d +%s) # BSD equivalent
+                WEEKOLDDATE=$(date -v-7d +%s) # BSD equivalent
             fi
             PARENTDATE=$(git show -s --format=%ct HEAD~1)
             if [[ $PARENTDATE -lt $WEEKOLDDATE ]]; then