Auto merge of #4543 - nerdrew:master, r=matklad
authorbors <bors@rust-lang.org>
Thu, 28 Sep 2017 07:47:38 +0000 (07:47 +0000)
committerbors <bors@rust-lang.org>
Thu, 28 Sep 2017 07:47:38 +0000 (07:47 +0000)
teach zsh completion +{stable,beta,nightly}

e.g.: `cargo +nightly test`


Trivial merge