_match.rs: fix module doc comment
_match.rs: fix module doc comment

It was applied to a `use` item, not to the module

aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,aidancully/rust,aidancully/rust,graydon/rust,graydon/rust,graydon/rust,aidancully/rust,graydon/rust