Sommer/Winter time with Jobs

[Bibo-Joshi]

Steps to reproduce

1. Live in Europe

2. Run a weekly job with something like

first = datetime(foo)
job_queue.run_repeating(job,
                        interval = timedelta(7),
                        first = first)

Expected behaviour

Job runs once a week at the specified time

Actual behaviour

The clock change from winter to sommer time is not handled correctly and the job runs an hour early/late.

Proposal:

Since the problem occurs only twice a year and is easily fixed by restarting the bot and this nonsence of constantly changing clocks hopefully ends by 2021, I guess this can be "fixed" by documenting it in the docstring of JobQueue.run_daily() and JobQueue.run_repeating().
If I get a LGTM for this "solution", I'll open a PR for it :)

[tsnoam]

@Bibo-Joshi
Thanks for the report. The documentation will be fixed.