Adjust build-stamp to always reflect the most recent tag

stamp.sh

@@ -1,10 +1,11 @@
 #!/bin/bash
 
-# Use the first tag that points to the current HEAD
-# if no tag is found, the latest git commit is used as a fallback
+# Use the first tag that points to the current HEAD. If no tag is found, the
+# summary given by `git describe` is used as a fallback (it contains the most
+# recent tag name, the number of commits since, and the short git hash).
 
 CURRENT_TAG=$(git tag -l --points-at HEAD | head -n1)
-CURRENT_COMMIT=$(git rev-parse HEAD)
+CURRENT_COMMIT=$(git describe --tags HEAD)
 
 echo "STABLE_VERSION ${CURRENT_TAG:-$CURRENT_COMMIT}"
 # rules_nodejs expects to read from volatile-status.txt