[1451] a minor editorial fix

src/bin/ddns/b10-ddns.xml

@@ -107,7 +107,7 @@
       <varname>zones</varname>
       The zones option is a named set of zones that can be updated with
       DDNS. Each entry has one element called update_acl, which is
-      is a list of access control rules that define update permissions.
+      a list of access control rules that define update permissions.
       By default this is empty; DDNS must be explicitely enabled per zone.
     </para>