DOC: Example of DataFrame.to_csv() is not showing properly
#### Problem description

Example of DataFrame.to_csv() is not showing properly. See the screenshoot below:

![Screenshot_20200130_130131](https://user-images.githubusercontent.com/1920463/73466588-d48aa980-4360-11ea-9432-6e52155fb00d.png)

#### Expected Output

I'll propose a PR fixing the docstring
