Fix an allday schedule bug.

Create an allday schedule on 2014/06/06 in google calender and type "M-x
org-gcal-fetch".
Then I get following status.
'2014-06-05' in google calendar
'<2014-06-05>--<2014-06-06>' in org-mode.
Merge pull request #22 from kenbeese/fix-allday-schedule

Fix an allday schedule bug.