fix typo in psql version number in indirect restore procedure

Not sure where psql 11 comes from here.

tsa/howto/postgresql.mdwn

@@ -169,7 +169,7 @@ server to the database server and restores from those.
     by name should be enough to find the latest one. Uncompress the
     `BASE` file in place:
 
-        cat ~postgres/restore/$CLIENT/main.BASE.bungei.torproject.org-20190805-145239-$CLIENT.torproject.org-main-9.6-backup.tar.gz | su postgres -c 'tar -C /var/lib/postgresql/11/main -x -z -f -'
+        cat ~postgres/restore/$CLIENT/main.BASE.bungei.torproject.org-20190805-145239-$CLIENT.torproject.org-main-9.6-backup.tar.gz | su postgres -c 'tar -C /var/lib/postgresql/9.6/main -x -z -f -'
 
     (Use `pv` instead of `cat` for a progress bar with large backups.)