use 2 semicolons in tal expression.

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@17250 20353a03-c40f-0410-a6d1-a30d3c3de9de

bt5/erp5_ical_style/SkinTemplateItem/portal_skins/erp5_ical_style/template_ical_style.xml

@@ -48,7 +48,7 @@
             <key> <string>_text</string> </key>
             <value> <string encoding="cdata"><![CDATA[
 
-<tal:block tal:define="dummy python:request.RESPONSE.setHeader(\'Content-Type\', \'text/calendar; charset=utf-8\');"\n
+<tal:block tal:define="dummy python:request.RESPONSE.setHeader(\'Content-Type\', \'text/calendar;; charset=utf-8\');"\n
 ><tal:block tal:define="listbox python:form[\'listbox\'];" \n
 ><tal:block tal:content="structure python: listbox.render()" />\n
 </tal:block>\n