Summary:
This gets us on the latest Prettier 2.x:
https://prettier.io/blog/2020/03/21/2.0.0.html
Notably, this adds support for TypeScript 3.8,
which introduces new syntax, such as `import type`.
Reviewed By: zertosh
Differential Revision: D20636268
fbshipit-source-id: fca5833d003804333a05ba16325bbbe0e06d6c8a