clarify the version-gate used for the #3229 change
clarify the version-gate used for the #3229 change

rust-lang/rustfmt,aidancully/rust,aidancully/rust,graydon/rust,SingingTree/rustfmt,graydon/rust,graydon/rust,SingingTree/rustfmt,graydon/rust,rust-lang/rustfmt,graydon/rust,aidancully/rust,aidancully/rust,aidancully/rust,aidancully/rust,graydon/rust