Fix weird spacing in error message.

Seems to have been introduced in 1a3458b6.

src/backend/port/sysv_shmem.c

@@ -392,7 +392,7 @@ CreateAnonymousSegment(Size *size)
 				 errhint("This error usually means that PostgreSQL's request "
 					"for a shared memory segment exceeded available memory, "
 					  "swap space or huge pages. To reduce the request size "
-						 "(currently  %zu bytes), reduce PostgreSQL's shared "
+						 "(currently %zu bytes), reduce PostgreSQL's shared "
 					   "memory usage, perhaps by reducing shared_buffers or "
 						 "max_connections.",
 						 *size) : 0));