use right variable name

buildimage.sh

@@ -14,7 +14,7 @@ IMAGENAME="$5/goemaxima:$3"
 # check if the image already exists on the server
 docker pull "${IMAGENAME}"
 # build it
-if [ "$stack" = "2017121800" ]; then
+if [ "$3" = "2017121800" ]; then
 	docker build -t "${IMAGENAME}" --build-arg MAXIMA_VERSION="$2" --build-arg SBCL_VERSION="$1" --build-arg LIB_PATH="$4" --build-arg "MAX_LIB_PATH=/opt/maxima/assets/maximalocal.mac" . || exit 1
 else
 	docker build -t "${IMAGENAME}" --build-arg MAXIMA_VERSION="$2" --build-arg SBCL_VERSION="$1" --build-arg LIB_PATH="$4" . || exit 1