updated travis to not push docker except for merges

Author: fehguy

.travis.yml

@@ -11,8 +11,7 @@ install:
 
 script:
   - mvn clean package
-  - docker build -t $DOCKER_IMAGE_NAME .
-  - if [ ! -z "$TRAVIS_TAG" ]; then docker tag $DOCKER_IMAGE_NAME:latest $DOCKER_IMAGE_NAME:$TRAVIS_TAG; fi && docker push $DOCKER_IMAGE_NAME
+  - if [ $DOCKERHUB_USERNAME ]; then echo docker login --email=$DOCKER_HUB_EMAIL --username=$DOCKER_HUB_USERNAME --password=$DOCKER_HUB_PASSWORD && echo docker build -t $DOCKER_IMAGE_NAME ./modules/swagger-generator && if [ ! -z "$TRAVIS_TAG" ]; then echo docker tag $DOCKER_IMAGE_NAME:latest $DOCKER_IMAGE_NAME:$TRAVIS_TAG; fi && echo docker push $DOCKER_IMAGE_NAME; fi
 
 env:  
   - DOCKER_IMAGE_NAME=swaggerapi/swagger-validator