message: avoid rebuilding Miri on CI
diff: @@ -7,10 +7,11 @@ if [ "$TRAVIS_OS_NAME" == osx ]; then
  else
  FOREIGN_TARGET=i686-unknown-linux-gnu
  fi
  +export CARGO_EXTRA_FLAGS="--all-features"
  # Prepare
  echo "Build and install miri"
  -./miri build --all-features --all-targets
  +./miri build --all-targets
  ./miri install
  echo
  