Update the description of type of check_option reloption in docs.

Commit 773df883 changed the type of check_option reloption
from string to enum. But it forgot to update the description of
the type in the documentation.

Author: Atsushi Torikoshi
Discussion: https://postgr.es/m/CACZ0uYFvHF4n6yxF390YZgr4Q0Z0c2w0ihu=DLb8ipNOnNcqzQ@mail.gmail.com

doc/src/sgml/ref/alter_view.sgml

@@ -143,7 +143,7 @@ ALTER VIEW [ IF EXISTS ] <replaceable class="parameter">name</replaceable> RESET
       Sets or resets a view option.  Currently supported options are:
       <variablelist>
        <varlistentry>
-        <term><literal>check_option</literal> (<type>string</type>)</term>
+        <term><literal>check_option</literal> (<type>enum</type>)</term>
         <listitem>
          <para>
           Changes the check option of the view.  The value must

doc/src/sgml/ref/create_view.sgml

@@ -131,7 +131,7 @@ CREATE VIEW [ <replaceable>schema</replaceable> . ] <replaceable>view_name</repl
 
       <variablelist>
        <varlistentry>
-        <term><literal>check_option</literal> (<type>string</type>)</term>
+        <term><literal>check_option</literal> (<type>enum</type>)</term>
         <listitem>
          <para>
           This parameter may be either <literal>local</literal> or