Apply suggestions from code review

Co-authored-by: Tim Head <[email protected]>

Author: consideRatio

ci/publish

@@ -44,7 +44,7 @@ if [ "${TRAVIS_TAG:-}" == "" ]; then
     #       we craft a commit message like jupyterhub/binderhub#123 or
     #       jupyterhub/binderhub@123abcd which will be understood as a reference
     #       by GitHub.
-    PR_OR_HASH=$(git log -1 --pretty=%B | head -n1 | sed 's/^.*\(#[0-9]*\).*/\1/' | sed 's/^\([0-9a-f]*\)-.*/@\1/')
+    PR_OR_HASH=$(git log -1 --pretty=%h-%B | head -n1 | sed 's/^.*\(#[0-9]*\).*/\1/' | sed 's/^\([0-9a-f]*\)-.*/@\1/')
     LATEST_COMMIT_TITLE=$(git log -1 --pretty=%B | head -n1)
     EXTRA_MESSAGE="${TRAVIS_REPO_SLUG}${PR_OR_HASH} ${LATEST_COMMIT_TITLE}"
     chartpress --push --publish-chart --long --extra-message "${EXTRA_MESSAGE}"