Update changelog for #67

Author: phil-opp

CHANGELOG.md

@@ -5,6 +5,8 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 
 ## Unreleased
 
+- Add an environment variable to keep the temp dir ([#67](https://github.com/rust-osdev/cargo-xbuild/pull/67))
+
 ## 0.5.28 - 2020-02-21
 
 - Update dependencies ([#65](https://github.com/rust-osdev/cargo-xbuild/pull/65))