erp5_wendelin: Update import for rfc1123_date

  Follow up the suggestion of the warning:

    <portal_components/document.erp5.DataArray>:31: DeprecationWarning: rfc1123_date is deprecated. Please import from App.Common.

bt5/erp5_wendelin/DocumentTemplateItem/portal_components/document.erp5.DataArray.py

@@ -28,7 +28,7 @@ from wendelin.bigarray.array_zodb import ZBigArray
 from erp5.component.document.File import _MARKER
 from wendelin.bigarray.array_ram import RAMArray
 from ZPublisher import HTTPRangeSupport
-from webdav.common import rfc1123_date
+from App.Common import rfc1123_date
 from DateTime import DateTime
 from mimetools import choose_boundary
 import transaction