Fix pg_replication_slot example output

The example output of pg_replication_slot is wrong.  Correct it and make
the output stable by explicitly listing columns to output.

Author: Kyotaro Horiguchi <horiguchi.kyotaro@lab.ntt.co.jp>
Reviewed-by: Michael Paquier <michael@paquier.xyz>
Discussion: https://postgr.es/m/20180731.190909.42582169.horiguchi.kyotaro@lab.ntt.co.jp

doc/src/sgml/high-availability.sgml

@@ -960,10 +960,10 @@ postgres=# SELECT * FROM pg_create_physical_replication_slot('node_a_slot');
 -------------+-----
  node_a_slot |
 
-postgres=# SELECT * FROM pg_replication_slots;
-  slot_name  | slot_type | datoid | database | active | xmin | restart_lsn | confirmed_flush_lsn
--------------+-----------+--------+----------+--------+------+-------------+---------------------
- node_a_slot | physical  |        |          | f      |      |             |
+postgres=# SELECT slot_name, slot_type, active FROM pg_replication_slots;
+  slot_name  | slot_type | active 
+-------------+-----------+--------
+ node_a_slot | physical  | f
 (1 row)
 </programlisting>
      To configure the standby to use this slot, <varname>primary_slot_name</>