Set gen_random_uuid() to volatile

It was set to immutable.  This was a mistake in the initial
commit (5925e55).

Reported-by: hubert depesz lubaczewski <depesz@depesz.com>
Discussion: https://www.postgresql.org/message-id/flat/20200218185452.GA8710%40depesz.com

Author: petere

src/include/catalog/catversion.h

@@ -53,6 +53,6 @@
  */
 
 /*							yyyymmddN */
-#define CATALOG_VERSION_NO	202002071
+#define CATALOG_VERSION_NO	202002191
 
 #endif

src/include/catalog/pg_proc.dat

@@ -8421,8 +8421,8 @@
   proname => 'uuid_hash_extended', prorettype => 'int8',
   proargtypes => 'uuid int8', prosrc => 'uuid_hash_extended' },
 { oid => '3432', descr => 'generate random UUID',
-  proname => 'gen_random_uuid', proleakproof => 't', prorettype => 'uuid',
-  proargtypes => '', prosrc => 'gen_random_uuid' },
+  proname => 'gen_random_uuid', proleakproof => 't', provolatile => 'v',
+  prorettype => 'uuid', proargtypes => '', prosrc => 'gen_random_uuid' },
 
 # pg_lsn
 { oid => '3229', descr => 'I/O',