added docker push from travis

.travis.yml

@@ -16,3 +16,13 @@ deploy:
     tags: true
     repo: swagger-api/swagger-ui
     node: '6.9'
+after_success:
+  - if [ $DOCKER_HUB_USERNAME ]; then 
+      docker login --email=$DOCKER_HUB_EMAIL --username=$DOCKER_HUB_USERNAME --password=$DOCKER_HUB_PASSWORD;
+      docker build -t $DOCKER_IMAGE_NAME .;
+      if [ "$TRAVIS_TAG" != "master" && -z "$TRAVIS_TAG"]; then
+        docker tag $DOCKER_IMAGE_NAME $DOCKER_IMAGE_NAME:$TRAVIS_TAG;
+      fi;
+
+      docker push $DOCKER_IMAGE_NAME;
+    fi;