dialplan: typo a/an script

src/modules/dialplan/doc/dialplan_admin.xml

@@ -610,7 +610,7 @@ xlog("the attributes associated with '+49$rU' are '$var(attrs)'\n");
 			<para><emphasis>script var</emphasis> </para>
 			<para>
 			- At input the function will get the input string from an existing
-			script variable. At output the function will set an script variable
+			script variable. At output the function will set a script variable
 			with the value of the output string.
 			</para>
 			</listitem>