update tag logic to `latest` and `unstable`

.travis.yml

@@ -23,11 +23,18 @@ deploy:
 after_success:
   - if [ $DOCKER_HUB_USERNAME ]; then 
       docker login --email=$DOCKER_HUB_EMAIL --username=$DOCKER_HUB_USERNAME --password=$DOCKER_HUB_PASSWORD;
-      docker build -t $DOCKER_IMAGE_NAME .;
+
       if [ ! -z "$TRAVIS_TAG" ]; then
-        docker tag $DOCKER_IMAGE_NAME:latest $DOCKER_IMAGE_NAME:$TRAVIS_TAG;
+        DOCKER_IMAGE_TAG=$TRAVIS_TAG;
+      else
+        DOCKER_IMAGE_TAG=unstable;
       fi;
-      if [ ! -z "$TRAVIS_TAG" ] || [ "$TRAVIS_BRANCH" = "master" ]; then
-        docker push $DOCKER_IMAGE_NAME;
+      docker build -t $DOCKER_IMAGE_NAME .;
+      if [ ! -z "$TRAVIS_TAG" ]; then
+        docker tag $DOCKER_IMAGE_NAME $DOCKER_IMAGE_NAME:$TRAVIS_TAG;
+        docker tag $DOCKER_IMAGE_NAME $DOCKER_IMAGE_NAME:latest;
+      else
+        docker tag $DOCKER_IMAGE_NAME:unstable $DOCKER_IMAGE_NAME:$unstable;
       fi;
     fi;
+