Invalid Typescript Types in lib/index.d.ts since 7.6.0

## Bug Report

**Current Behavior**
`node_modules/@babel/types/lib/index.d.ts` has invalid typescript since the 7.6.0 release: https://unpkg.com/browse/@babel/types@7.6.0/lib/index.d.ts line 2098

```
export function isNode(node: ?object): boolean
```

**Environment**
- Babel version(s): 7.6.0

**Possible Solution**
Move the `?` before the `:`

