Auto merge of #7513 - Eh2406:ci, r=ehuss
Auto merge of #7513 - Eh2406:ci, r=ehuss

don't download std-docs on CI

Now that we have a way to do it, lets not download std-docs on CI. Based on the blog post:
https://blog.rust-lang.org/2019/10/15/Rustup-1.20.0.html

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