doc fix for KLDivLoss (#36137)
Summary:
Fixes doc for KLDivLoss as per [this comment](https://github.com/pytorch/pytorch/pull/34586#discussion_r404442741).
Pull Request resolved: https://github.com/pytorch/pytorch/pull/36137
Differential Revision: D20932395
Pulled By: gchanan
fbshipit-source-id: ecc395e6bc689fbf758e2cdca946049de8963856
