DOC: default value for pd.DateOffset() is 24 hours instead of 1 calendar day
```python
>>>pd.__version__
1.1.1
>>>ts = pd.Timestamp('2011-3-27 00:00:00', tz='Europe/Helsinki')
>>>ts + pd.DateOffset(days=1)
Timestamp('2011-03-28 00:00:00+0300', tz='Europe/Helsinki')
>>>ts + pd.DateOffset()
Timestamp('2011-03-28 01:00:00+0300', tz='Europe/Helsinki')
>>>ts + pd.DateOffset(hours=24)
Timestamp('2011-03-28 01:00:00+0300', tz='Europe/Helsinki')
```

The default action for pd.DateOffset seems to be equal to pd.DateOffset(hours=24) instead of pd.DateOffset(days=1).
But the user guide says DateOffset object defaults to 1 calendar day.

<img width="611" alt="捕获" src="https://user-images.githubusercontent.com/41546976/93727690-db677480-fbee-11ea-9439-24979ebb85ce.PNG">