Update ci-automation/az_sig_publish.sh

Co-authored-by: James Le Cuirot <jlecuirot@microsoft.com>

Author: sayanchowdhury

ci-automation/az_sig_publish.sh

@@ -29,7 +29,7 @@ function _az_sig_publish_impl() {
   fi
 
   FLATCAR_GALLERY_IMAGE_NAME="flatcar-${channel}-${arch}"
-  version=$(echo "${vernum}" | cut -d '-' -f2)
+  version=$(cut -d '-' -f2 <<< "${vernum}")
 
   local date=""
   if [[ "$vernum" == *nightly* ]]; then