Auto merge of #5802 - ehuss:fix-doc-typo, r=dwijnand
Auto merge of #5802 - ehuss:fix-doc-typo, r=dwijnand

Fix minor typo in the book.

rustyhorde/cargo,tsurai/cargo,tshepang/cargo,eminence/cargo,eminence/cargo,rust-lang/cargo,rust-lang/cargo,tshepang/cargo,rustyhorde/cargo,rust-lang/cargo,tsurai/cargo,tsurai/cargo,eminence/cargo,tshepang/cargo,rustyhorde/cargo,rustyhorde/cargo,nipunn1313/cargo,tsurai/cargo,nipunn1313/cargo,tshepang/cargo,tsurai/cargo,vojtechkral/cargo,vojtechkral/cargo,eminence/cargo,nipunn1313/cargo,nipunn1313/cargo,rust-lang/cargo,vojtechkral/cargo,vojtechkral/cargo