Summary:
In #1194, we upgraded Prettier from 1.13.4 to 1.18.2, but this upgrades
past <https://github.com/prettier/prettier/pull/5647>, which was first
released in Prettier 1.16.0. This commit fixes the uses of deprecated
code introduced as a result. It also upgrades the type definitions to
match, via `flow-typed install prettier@1.18.2`.
Addresses part of #1308.
Test Plan:
Prior to this commit, running `yarn unit` would print
```
console.warn node_modules/prettier/index.js:7934
{ parser: "babylon" } is deprecated; we now treat it as { parser: "babel" }.
```
in two test cases; it no longer prints any such warnings. Furthermore,
running `git grep 'parser.*babylon'` no longer finds any matches.
wchargin-branch: prettier-deprecations
c162813a5e