Fix latex formular error about *normal (#21000)
Summary:
issue:
https://github.com/pytorch/pytorch/issues/20903
the latex abort norm should be `\mathcal{N}(\text{mean}, \text{std}^2)`
Pull Request resolved: https://github.com/pytorch/pytorch/pull/21000
Differential Revision: D15695335
Pulled By: ezyang
fbshipit-source-id: 34dcca0acb20c297f876287e081cd44d11a3e516
