Hashbang comments are stripped from JS output

This is a followup to #541. Most cases were fixed when the issue was solved, except for hashbangs at the start of the file. Those are still omitted from the JS output, even when `removeComments` is `false`.

For example:
TS:
```ts
#!/usr/bin/env node

// ...code
```

JS:
```js
// ...code
```
