Fixes tag cmd (#464)

Author: David Ansermino

scripts/ci_docker.sh

@@ -7,7 +7,7 @@ set -ex
 GIT_SHORT_COMMIT=`git rev-parse --short HEAD`
 TIMESTAMP=`date -u +%Y%m%d%H%M%S`
 IMAGE_NAME="chainsafe/chainbridge"
-TAG="${TIMESTAMP}-${GIT_SHORT_COMMIT}"
+TAG=${TAG:-"${TIMESTAMP}-${GIT_SHORT_COMMIT}"}
 
 case $TARGET in
   "default")
@@ -22,7 +22,7 @@ case $TARGET in
   "release")
     echo "Pushing image with tag $TAG"
     docker build $BUILD_ARGS -t ${IMAGE_NAME}:${TAG} .
-    docker tag "${IMAGE_NAME}:${TAG}"
+    docker tag "${IMAGE_NAME}:${TAG}" "${IMAGE_NAME}:latest"
     echo "$DOCKER_PASSWORD" | docker login -u "$DOCKER_USERNAME" --password-stdin
     docker push ${IMAGE_NAME}:${TAG}
     ;;