DOC: Fix whatsnew contributors section
Was reading over the whatsnew and noticed that the [1.0 Contributors section 
](https://dev.pandas.io/docs/whatsnew/v1.0.0.html#contributors) is empty, and the [0.25.3 Contributors section](https://dev.pandas.io/docs/whatsnew/v0.25.3.html#contributors) looks way to big.