Trivial changes in the Rust book.

[ticki]

Just some small changes.

[rust-highfive]

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[ticki]

Thank you, my fellow bot.

[steveklabnik]

this should be in graves, not apostraphes, see line 101 and 102 above

[steveklabnik]

one tiny nit, otherwise r=me

[ticki]

Done.

[steveklabnik]

@bors: r+ rollup

[bors]

📌 Commit cf1e078 has been approved by steveklabnik

[steveklabnik]

Thank you!

[ticki]

Yes, you bots are so friendly.