Remove excess semicolon in MERGE docs

Author: Euler Taveira <euler@eulerto.com>
Discussion: https://postgr.es/m/01dea9ef-85ad-4e09-a783-a1eadeae7bbe@www.fastmail.com

Author: alvherre

doc/src/sgml/ref/merge.sgml

@@ -596,7 +596,7 @@ ON s.winename = w.winename
 WHEN NOT MATCHED AND s.stock_delta > 0 THEN
   INSERT VALUES(s.winename, s.stock_delta)
 WHEN MATCHED AND w.stock + s.stock_delta > 0 THEN
-  UPDATE SET stock = w.stock + s.stock_delta;
+  UPDATE SET stock = w.stock + s.stock_delta
 WHEN MATCHED THEN
   DELETE;
 </programlisting>