Honor single-day OOOs without needing a range

[JamesMGreene]

I would be nice to honor single-day OOOs without needing to specify a range.

For example, this works:

/ooo from 6/19 to 6/19

But this does not:

/ooo on 6/19

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I used the same sherlockjs parser in my Services spreadsheet-updating Action (internal to GitHub) and, when parsing such a command, it does parse out a startDate but not an endDate. So, basically, if you ended up in that situation, I would suggest filling in the default value of endDate as being at "23:59:59.999Z" on the same UTC date as startDate.