Edit rustc_middle::lint::LintSource docs
Edit rustc_middle::lint::LintSource docs

Edit punctuation in doc comment for rustc_middle::lint::LintSource::CommandLine.

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