man: fix default value in resolved.conf man page (systemd#10733)

AlexanderKurtz · yuwata · commit f628e3eea7cf · 2018-11-12T15:44:55.000+09:00
See https://github.com/systemd/systemd/blob/v239/meson_options.txt#L190
diff --git a/man/resolved.conf.xml b/man/resolved.conf.xml
@@ -189,7 +189,7 @@
         domains (TLDs) that are not known by the DNS root server. This
         logic does not work in all private zone setups.</para>
 
-        <para>Defaults to off.</para>
+        <para>Defaults to <literal>allow-downgrade</literal></para>
         </listitem>
       </varlistentry>
 
