DOC: Fix versionchanged directive in DataFrame.plot

[datapythonista]

Looks like there is something wrong in the documentation of DataFrame.plot, and the .. versionchanged directive of the parameters logx, logy and loglog is not rendered correctly: https://pandas.pydata.org/docs/dev/reference/api/pandas.DataFrame.plot.html

It's probably a typo, a missing space or something. We should have a look and compare with another docstring where a parameter versionchanged is correctly rendered, see what's wrong, and fix it.

[Shikharishere]

Hey, @datapythonista shikhar here, can you guide me through this issue?

[mathpn]

It seems that the issue is caused by a lack of a blank new line. All others ".. versionchanged" occurrences have a blank line before. I've created a pull request with this tiny change. Considering how tiny it is, I haven't included anything in the changelog, please tell me if that's OK.