Auto merge of #4911 - phansch:update_changelog, r=flip1995
Auto merge of #4911 - phansch:update_changelog, r=flip1995

Update changelog for Rust 1.39 and 1.40

[Rendered](https://github.com/phansch/rust-clippy/blob/update_changelog/CHANGELOG.md)

changelog: none

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