Fix typo in docs.

Reported-by: Darko Prelec

doc/src/sgml/parallel.sgml

@@ -240,7 +240,7 @@ EXPLAIN SELECT * FROM pgbench_accounts WHERE filler LIKE '%x%';
     copy of the output result set, so the query would not run any faster
     than normal but would produce incorrect results.  Instead, the parallel
     portion of the plan must be what is known internally to the query
-    optimizer as a <firstterm>partial plan</>; that is, it must constructed
+    optimizer as a <firstterm>partial plan</>; that is, it must be constructed
     so that each process which executes the plan will generate only a
     subset of the output rows in such a way that each required output row
     is guaranteed to be generated by exactly one of the cooperating processes.