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 rust-lang/miri#713).  That should not lead to hashbrown's CI failing.

Cc @gnzlbg

Author: bors

Diff for: ci/miri.sh

@@ -5,7 +5,6 @@ set -ex
 export CARGO_NET_RETRY=5
 export CARGO_NET_TIMEOUT=10
 
-if rustup component add miri ; then
-    cargo miri setup
+if rustup component add miri && cargo miri setup ; then
     cargo miri test -- -- -Zunstable-options --exclude-should-panic
 fi