Wrong span when parse TypeTuple with more than two elements

[imlk0]

when parsing the string text:

    let text = r#"
        (usize, usize, usize, usize, usize, usize)
    "#;

the result of to_token_stream():

    let tuple: TypeTuple = syn::parse_str(text).unwrap();
    let ts = tuple.to_token_stream();

and TokenStream::from_str(text)

    let ts: TokenStream = TokenStream::from_str(text).unwrap();

are not the same.

Specifically, except for the first comma, the results of.span() on the remaining commas are the same.
All results of span.start() and span.end() are LineColumn { line: 1, column: 0 }

This may cause misunderstandings to those who think that .to_token_stream() is equivalent to TokenStream::from_str(text)

playground: https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=5161bd64cbd54d283bcf04b47cec8343

[dtolnay]

Thanks, I've published a fix in 1.0.59.