Fix full_version setting in push-images.sh CTR

The JANUS_VERSION is now set as an ARG and not an ENV any more in the
Dockerfiles.

Signed-off-by: Florian Hockmann <fh@florian-hockmann.de>

push-images.sh

@@ -11,7 +11,7 @@ latest_version=${versions[${#versions[@]}-1]}
 for v in "${versions[@]}"; do
   if [ -z "${version}" ] || [ "${version}" == "${v}" ]; then
     # read full version from Dockerfile
-    full_version=$(grep "ENV JANUS_VERSION" ${v}/Dockerfile | cut -d"=" -f 2)
+    full_version=$(grep "ARG JANUS_VERSION" ${v}/Dockerfile | cut -d"=" -f 2)
     # push relevant tags
     docker push "janusgraph/janusgraph:${full_version}"
     docker push "janusgraph/janusgraph:${v}"