Update .prettierrc.json to include trailingComma: all to match internal Google config

[calebegg]

fixes #662

[tonycoco]

Can we rebase this? Change looks good to me.

[calebegg]

I am not good at git, my brain has been permanently disfigured by fifteen years of using nothing but Piper/Perforce. I think I screwed this up somehow even though I was following a github help page. If you want to help me that's fine, or if you want to just make the change yourself that's fine too. I've spent half an hour on this and I'm quite frustrated.

[calebegg]

Ok I think I fixed it (thanks again for the help!)

[tonycoco]

Note: the commit message needs to follow conventional commits. Can you amend your commit message?

This change will be messy for lots of repos using gts so we should think about bumping the release semver to align.

[calebegg]

Done