Dataframe.median and Dataframe.mean documentation
https://pandas-docs.github.io/pandas-docs-travis/generated/pandas.DataFrame.median.html?highlight=dataframe%20median#pandas.DataFrame.median

```python
DataFrame.median(axis=None, skipna=None, level=None, numeric_only=None, **kwargs)
```
#### Issue:

**skipna** shows as **_None_** in the code above but in the parameters it says 'skipna : boolean, default True'. So should it say **_True_** in the line above? Maybe I'm wrong, feel free to correct me!

Same for dataframe.mean:
https://pandas-docs.github.io/pandas-docs-travis/generated/pandas.DataFrame.mean.html?highlight=dataframe%20mean#pandas.DataFrame.mean

