[Update] Exit with fancy error when branch is empty

update.sh

@@ -26,6 +26,7 @@ DATE=$(date +%Y-%m-%d_%H_%M_%S)
 BRANCH=$(git rev-parse --abbrev-ref HEAD)
 
 function prefetch_images() {
+  [[ -z ${BRANCH} ]] && { echo -e "\e[33m\nUnknown branch...\e[0m"; exit 1; }
   while read image; do
     RET_C=0
     until docker pull ${image}; do