Keep environment variables in a BTreeMap to preserve sort order
Keep environment variables in a BTreeMap to preserve sort order

This prevents verbose output from varying between runs due to HashMap
(non-)ordering.

rust-lang/cargo,rust-lang/cargo,rust-lang/cargo,nipunn1313/cargo,eminence/cargo,vojtechkral/cargo,rustyhorde/cargo,vojtechkral/cargo,nipunn1313/cargo,nipunn1313/cargo,tshepang/cargo,tsurai/cargo,nipunn1313/cargo,eminence/cargo,rustyhorde/cargo,tshepang/cargo,tshepang/cargo,tsurai/cargo,vojtechkral/cargo,vojtechkral/cargo,tsurai/cargo,tsurai/cargo,rust-lang/cargo,rustyhorde/cargo,rustyhorde/cargo,tsurai/cargo,eminence/cargo,eminence/cargo,tshepang/cargo