DOC: Fix mistake in code example

[huang06]

Location of the documentation

https://pandas.pydata.org/docs/user_guide/timeseries.html#working-with-time-zones

import datetime
import pytz

datetime.datetime(2011, 1, 1, tz=pytz.timezone('US/Eastern'))

TypeError: 'tz' is an invalid keyword argument for this function

Replace tz with tzinfo can fix it.

import datetime
import pytz
datetime.datetime(2011, 1, 1, tzinfo=pytz.timezone('US/Eastern'))

datetime.datetime(2011, 1, 1, 0, 0, tzinfo=<DstTzInfo 'US/Eastern' LMT-1 day, 19:04:00 STD>)

[MarcoGorelli]

thanks @huang06