invalidate ci cache

Author: jstarry

.buildkite/hooks/pre-command

@@ -19,7 +19,8 @@ pattern='^[0-9]+\.[0-9]+\.[0-9]+$'
 if [[ ${HOST_RUST_VERSION} =~ ${pattern} ]]; then
     HOST_RUST_VERSION="${rust_stable%.*}"
 fi
-export CARGO_TARGET_CACHE=$HOME/cargo-target-cache/"$CHANNEL"-"$BUILDKITE_LABEL"-"$SBF_TOOLS_VERSION"-"$HOST_RUST_VERSION"
+CACHE_VERSION=1 # bump version to invalidate caches
+export CARGO_TARGET_CACHE=$HOME/cargo-target-cache/"$CHANNEL"-"$BUILDKITE_LABEL"-"$SBF_TOOLS_VERSION"-"$HOST_RUST_VERSION"-"$CACHE_VERSION"
 (
   set -x
   MAX_CACHE_SIZE=18 # gigabytes