don't build pull request, just branches.

.travis.yml

@@ -24,7 +24,7 @@ script:
 jobs:
   include:
     - stage: deploy
-      if: branch = master OR branch =~ ^r[0-9]+.[0-9]+
+      if: (branch = master OR branch =~ ^r[0-9]+.[0-9]+) AND type != pull_request
       script:
       - echo "$DOCKER_PASSWORD" | docker login -u "$DOCKER_USERNAME" --password-stdin
       - docker build -t "$TRAVIS_REPO_SLUG" .