fix minor grammar issue.

git-svn-id: svn://bind10.isc.org/svn/bind10/branches/trac341@2943 e5f2f494-b856-4b98-b285-d166d9295462

src/bin/xfrout/b10-xfrout.xml

@@ -54,7 +54,7 @@
     <title>DESCRIPTION</title>
     <para>The <command>b10-xfrout</command> daemon provides the BIND 10
       outgoing DNS zone transfer service.
-      It also used to send outgoing NOTIFY messages.
+      It is also used to send outgoing NOTIFY messages.
       Normally it is started by the
       <citerefentry><refentrytitle>bind10</refentrytitle><manvolnum>8</manvolnum></citerefentry>
       boss process.