fix #272

[alpha-beta-soup]

Fixes problem with nightshade checking whether a datetime is in UTC; it was rejecting datetimes that have their tzinfo explicitly set to UTC. The check has now been corrected and simplified.

In [37]: d = datetime.datetime.now()

In [38]: bool(d.utcoffset()) # time-zone naive
Out[38]: False

In [39]: d = d.replace(tzinfo=pytz.UTC)

In [40]: bool(d.utcoffset()) # utc
Out[41]: False

In [41]: eastern = pytz.timezone('US/Eastern')

In [42]: d = d.replace(tzinfo=eastern)

In [43]: bool(d.utcoffset()) # non-utc, non-zero offset
Out[43]: True

So therefore the check only needs to be if date.utcoffset():, which catches all non-zero offsets, and allows the naive case to continue passing.

[WeatherGod]

Thank you!