tsilo: fixed ts_append example in the doc

(cherry picked from commit 18ef9da4c029fefd5089aed484cd8f32ddb0fb17)
(cherry picked from commit f727b05ad76c1b22ddba8b3aed311084c260c588)

src/modules/tsilo/doc/tsilo_admin.xml

@@ -178,7 +178,7 @@ if (is_method("INVITE")) {
 		<programlisting format="linespecific">
 ...
 if (is_method("REGISTER")) {
-	ts_append("location", "$tU");
+	ts_append("location", "$tu");
 }
 ...
 </programlisting>