Only export path for linux
Only export path for linux

as per [@davidalber's advice](https://github.com/rust-lang-nursery/rustfmt/pull/2229#discussion_r155129274)
graydon/rust,graydon/rust,aidancully/rust,rust-lang/rustfmt,SingingTree/rustfmt,aidancully/rust,graydon/rust,aidancully/rust,aidancully/rust,aidancully/rust,SingingTree/rustfmt,graydon/rust,rust-lang/rustfmt,graydon/rust,aidancully/rust,graydon/rust