DOC: documentation link to whatsnew v1.0.4 not working
#### Location of the documentation

full whatsnew link on
https://github.com/pandas-dev/pandas/releases/tag/v1.0.4

#### Documentation problem

The link to https://pandas.pydata.org/docs/whatsnew/v1.0.4.html is not working though https://pandas.pydata.org/docs/whatsnew/v1.0.3.html works
