add missing import pytz in example

[abe-101]

The example uses the pytz module:
event.add('dtstart', datetime(2005,4,4,8,0,0,tzinfo=pytz.utc))
But doesn't import it

[coveralls]

Pull Request Test Coverage Report for Build 3734533904

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.0%) to 93.323%

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Totals
Change from base Build 3612230234:	-0.0%
Covered Lines:	1160
Relevant Lines:	1243

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💛 - Coveralls

[jacadzaca]

Every little bit helps, thanks :)