Doc: Fix order of pg_shmem_allocations in system view list

pg_shmem_allocations was in the wrong position with pg_stats.

Author: Ian Barwick
Discussion: https://postgr.es/m/de7279d4-7ea0-037f-d7d2-1161682339db@2ndquadrant.com

doc/src/sgml/catalogs.sgml

@@ -9309,13 +9309,13 @@ SCRAM-SHA-256$<replaceable>&lt;iteration count&gt;</replaceable>:<replaceable>&l
      </row>
 
      <row>
-      <entry><link linkend="view-pg-stats"><structname>pg_stats</structname></link></entry>
-      <entry>planner statistics</entry>
+      <entry><link linkend="view-pg-shmem-allocations"><structname>pg_shmem_allocations</structname></link></entry>
+      <entry>shared memory allocations</entry>
      </row>
 
      <row>
-      <entry><link linkend="view-pg-shmem-allocations"><structname>pg_shmem_allocations</structname></link></entry>
-      <entry>shared memory allocations</entry>
+      <entry><link linkend="view-pg-stats"><structname>pg_stats</structname></link></entry>
+      <entry>planner statistics</entry>
      </row>
 
      <row>