src/bin/backup: exclude ~/.cache from backup

For two reasons:
1. to reduce the size of the backup.  If there's a candidate folder to
   be removed in order to decrease the size of the backup, ~/.cache is
   that folder;
2. to stop errors during the backup to happen.  It's common for files to
   come and go while the backup is running, and borg sometimes starts
   backing up a file and it vanishes in the middle of the backup, and
   returns an error.  In the end the backup finishes sucessfully, but
   the backup script halts.

0 files changed, 0 insertions, 0 deletions