PG 10 release notes: update PL/Tcl functions item

Update attribution of PL/Tcl functions item from Jim Nasby to Karl
Lehenbauer.

Reported-by: Jim Nasby

Discussion: https://postgr.es/m/ed42f3d6-4251-dabc-747f-1ff936763b2b@nasby.net

Backpatch-through: 10

doc/src/sgml/release-10.sgml

@@ -2046,7 +2046,7 @@
 -->
        <para>
         Allow PL/Tcl functions to return composite types and sets
-        (Jim Nasby)
+        (Karl Lehenbauer)
        </para>
       </listitem>