minor grammatical update

[frankmcsherry]

Grammatical update (and passive -> active, but I'm not sure if "Rust" is often used as a subject in the book; feel free to revert that part for style, but keep the subject-verb agreement)

r? @steveklabnik

[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.

If any changes to this PR are deemed necessary, please add them as extra commits. This ensures that the reviewer can see what has changed since they last reviewed the code. The way Github handles out-of-date commits, this should also make it reasonably obvious what issues have or haven't been addressed. Large or tricky changes may require several passes of review and changes.

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[arielb1]

There's nothing wrong with the passive voice.

[steveklabnik]

I agree that the passive voice isn't inherently bad, but I also do think this is an improvement, thank you

[steveklabnik]

@bors: r+ rollup

[bors]

📌 Commit d673bde has been approved by steveklabnik

[bors]

⌛ Testing commit d673bde with merge 137a699...

[bors]

☀️ Test successful - auto-linux-32-nopt-t, auto-linux-32-opt, auto-linux-64-nopt-t, auto-linux-64-opt, auto-linux-64-x-android-t, auto-mac-32-opt, auto-mac-64-nopt-t, auto-mac-64-opt, auto-win-gnu-32-nopt-t, auto-win-gnu-32-opt, auto-win-gnu-64-nopt-t, auto-win-gnu-64-opt