withStorybook.d.ts file is not emitted

[trajano]

Describe the bug #633 switches to typescript which is good, but the code needs a change to get the typings correct in the .d.ts

As I noted in the comment @tlow92 you added the hack I did for .d.ts to export it as a function but it does not send the correct typing and the .d.ts emitted is actually not correct. So I had to patch it back to

export = withStorybook;

I think all you need to do as I had commented is is export function withStorybook and it will emit the .d.ts correctly.