Fix typo.

Jesper Pedersen

Discussion: http://postgr.es/m/000f92d6-f623-95a5-b341-46e2c0495cea@redhat.com

src/backend/utils/misc/postgresql.conf.sample

@@ -163,7 +163,7 @@
 #effective_io_concurrency = 1		# 1-1000; 0 disables prefetching
 #max_worker_processes = 8		# (change requires restart)
 #max_parallel_workers_per_gather = 2	# taken from max_parallel_workers
-#parallel_leader_particulation = on
+#parallel_leader_participation = on
 #max_parallel_workers = 8		# maximum number of max_worker_processes that
 					# can be used in parallel queries
 #old_snapshot_threshold = -1		# 1min-60d; -1 disables; 0 is immediate