[Update] Make the update check in update.sh readonly

update.sh

@@ -71,8 +71,12 @@ while (($#)); do
   case "${1}" in
     --check|-c)
       echo "Checking remote code for updates..."
-      git fetch origin #${BRANCH}
-      if [[ -z $(git log HEAD --pretty=format:"%H" | grep $(git rev-parse origin/${BRANCH})) ]]; then
+      LATEST_REV=$(git ls-remote --exit-code --refs --quiet https://github.com/mailcow/mailcow-dockerized ${BRANCH} | cut -f1)
+      if [ $? -ne 0 ]; then
+        echo "A problem occurred while trying to fetch the latest revision from github."
+        exit 99
+      fi
+      if [[ -z $(git log HEAD --pretty=format:"%H" | grep "${LATEST_REV}") ]]; then
         echo "Updated code is available."
         exit 0
       else