Fix typos in libsyntax/tokenstream.rs

[osa1]

No description provided.

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @nrc (or someone else) soon.

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[GuillaumeGomez]

Thanks!

@bors: r+ rollup

[bors]

📌 Commit 15411fb has been approved by GuillaumeGomez

[bors]

⌛ Testing commit 15411fb with merge c81c1d6...

[bors]

☀️ Test successful - status-appveyor, status-travis
Approved by: GuillaumeGomez
Pushing c81c1d6 to master...