Fix documentation of check_option in information_schema.views

Support of CHECK OPTION for updatable views has been added in 9.4, but
the documentation of information_schema never got the call even if the
information displayed is correct.

Author: Gilles Darold
Discussion: https://postgr.es/m/75d07704-6c74-4f26-656a-10045c01a17e@darold.net
Backpatch-through: 9.4

doc/src/sgml/information_schema.sgml

@@ -6640,7 +6640,11 @@ ORDER BY c.ordinal_position;
      <row>
       <entry><literal>check_option</literal></entry>
       <entry><type>character_data</type></entry>
-      <entry>Applies to a feature not available in <productname>PostgreSQL</></entry>
+      <entry>
+       <literal>CASCADED</literal> or <literal>LOCAL</literal> if the view
+       has a <literal>CHECK OPTION</literal> defined on it,
+       <literal>NONE</literal> if not
+      </entry>
      </row>
 
      <row>