Auto merge of #1193 - alex:patch-1, r=emilio
Auto merge of #1193 - alex:patch-1, r=emilio

Fixed rendering of a header in the book

rust-lang/rust-bindgen,emilio/rust-bindgen,rust-lang/rust-bindgen,emilio/rust-bindgen,rust-lang/rust-bindgen,emilio/rust-bindgen,emilio/rust-bindgen,rust-lang/rust-bindgen,emilio/rust-bindgen