prettier solidity formatting broken
I was looking at @stubbrn's PRs and they are failing the format check in CI.  

It looks like `prettier` made a 3.0 release 5 days ago that broke things for us:
https://github.com/prettier/prettier/releases

Downgrading to prettier 2.8.8 fixes the issue:
```shell
npm install --global --save-dev prettier@2.8.8
```
I [opened a ticket](https://github.com/prettier-solidity/prettier-plugin-solidity/issues/885) with the plugin developers. Unless they make a new release soon, we'll have to lock the prettier version at 2.8.8 so CI can pass.