Fix typo in recently-added TAP test for replication slots

Oversight in commit b0afdca.

Author: michaelpq

src/test/recovery/t/006_logical_decoding.pl

@@ -151,7 +151,7 @@
 my $logical_restart_lsn_pre = $node_master->safe_psql('postgres',
 	"SELECT restart_lsn from pg_replication_slots WHERE slot_name = '$logical_slot';");
 chomp($logical_restart_lsn_pre);
-# Slot advance should persists across clean restarts.
+# Slot advance should persist across clean restarts.
 $node_master->restart;
 my $logical_restart_lsn_post = $node_master->safe_psql('postgres',
 	"SELECT restart_lsn from pg_replication_slots WHERE slot_name = '$logical_slot';");