install Miri via rustup

Author: RalfJung

ci/miri.sh

@@ -5,7 +5,7 @@ set -ex
 export CARGO_NET_RETRY=5
 export CARGO_NET_TIMEOUT=10
 
-if cargo install --force --git https://github.com/rust-lang/miri miri ; then
+if rustup component add miri ; then
     cargo miri setup
     cargo miri test
 fi