Doc: clarify release note text about v11's new window function features.

Jonathan S. Katz

Discussion: https://postgr.es/m/30468663-E67D-4753-8269-7E6A4001A281@excoventures.com

Author: tglsfdc

doc/src/sgml/release-11.sgml

@@ -92,7 +92,7 @@
 
     <listitem>
      <para>
-      Window functions now support all options shown in the SQL:2011
+      Window functions now support all framing options shown in the SQL:2011
       standard, including <literal>RANGE <replaceable>distance</replaceable>
       PRECEDING/FOLLOWING</literal>, <literal>GROUPS</literal> mode, and
       frame exclusion options