Auto merge of #78 - RalfJung:miri, r=Amanieu
Auto merge of #78 - RalfJung:miri, r=Amanieu

skip Miri tests if the setup fails

Currently we are in a situation where Miri can be installed but `cargo miri setup` fails (due to https://github.com/rust-lang/miri/issues/713).  That should not lead to hashbrown's CI failing.

Cc @gnzlbg

rust-lang/hashbrown,rust-lang/hashbrown