Update tensorboard.rst (#22026)
Summary:
**Patch Description**:
Update the docs to reflect one no longer needs to install tensorboard nightly, as Tensorboard 1.14.0 was [released last week](https://github.com/tensorflow/tensorboard/releases/tag/1.14.0).
**Testing**:
Haven't actually tested pytorch with tensorboard 1.14 yet. I'll update this PR once I have.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/22026
Differential Revision: D16772136
Pulled By: orionr
fbshipit-source-id: 2e1e17300f304f50026837abbbc6ffb25704aac0
