TypeScript: cannot parse decorator + generator syntax

Howdy!
Thanks for creating recast 🙇
I found it troublesome to parse a code like this:
```typescript
export default class DocumentsService {
@abc({ on: 'init' })
*loadEndpoint() {
yield 'abc';
return 'foo';
};
};
```
The error is `SyntaxError: Unexpected token (3:16)`
A workaround is to explicitly declare the method as public

```typescript
export default class DocumentsService {
@abc({ on: 'init' })
public *loadEndpoint() {
yield 'abc';
return 'foo';
};
};
```

I created [a repository with minimal failing example](https://github.com/maciejmyslinski/recast-issue) so that you an try it out yourself.

I thought those issues with babel might be connected:
* https://github.com/babel/babel/issues/5704
* https://github.com/babel/babylon/issues/13

But they claimed this is fixed so I decided to report it here first.

Start by reproducing the TypeScript snippet in the linked minimal failing example, then compare it with the version that adds the public modifier. Trace the parsing entry point that reports the unexpected token; done means the decorator-plus-generator example parses successfully without requiring public.

Written by the indexing model from the issue text.