Fix build_artifact_protoc.sh to pass shellcheck
diff --git a/tools/run_tests/artifacts/build_artifact_protoc.sh b/tools/run_tests/artifacts/build_artifact_protoc.sh
index 5c5ab7d..b531fc9 100755
--- a/tools/run_tests/artifacts/build_artifact_protoc.sh
+++ b/tools/run_tests/artifacts/build_artifact_protoc.sh
@@ -18,7 +18,7 @@
 
 set -ex
 
-cd $(dirname $0)/../../..
+cd "$(dirname "$0")/../../.."
 
 make plugins