Auto merge of #5652 - rust-lang:flip1995-patch-1, r=yaahc
Auto merge of #5652 - rust-lang:flip1995-patch-1, r=yaahc

Fail bors on missing changelog

Bors stopped failed if the changelog was missing. Instead it waited 2h (?) and then timed out.

changelog: none

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