Bump TypeScript to 3.7

[bramkragten]

Adds optional chaining:

// Before
if (foo && foo.bar && foo.bar.baz) {
    // ...
}

// After-ish
if (foo?.bar?.baz) {
    // ...
}

And more:
https://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-7.html

Babel changelog: https://babeljs.io/blog/2019/11/05/7.7.0