docs: make some tiny modification about spelling

[tclfs]

I think it would be better after modification.

[rust-highfive]

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

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[steveklabnik]

I have always been a bit unsure about hyphen usage. I'm about to get on a plane, but I'm going to do some research on this later today; it's quite possible you're right 😄

[apasel422]

@steveklabnik For what it's worth, I agree with these changes.

[apasel422]

@bors: r+ rollup

[bors]

📌 Commit 2318e9f has been approved by apasel422