Retrieves the last build date from the feed.
[ lastBuildDate = ] Feed.LastBuildDate
lastBuildDate Floating-point number that receives the date and time of the last content change.
The property is read-only. The property has no default value.
Last build date is an optional feed element. The value is
0if not specified in the source.
A value of 0 is representative of the date "Sat Dec 30 00:00:00 PST 1899".
The date is adjusted for the local time zone.