Login to docker hub before pulling images (#2995)

.travis.yml

@@ -12,6 +12,7 @@ before_install:
   - date=`date +%Y%m%d%H%M%S` && branch=${TRAVIS_BRANCH} && rev=`git rev-parse --short=6
     HEAD` && sed -i "s/\$1/\$1.$date.$branch.$rev/g" deployment.json
 script:
+  - echo "$DOCKER_PASSWORD" | docker login -u "$DOCKER_USERNAME" --password-stdin
   - docker run --rm -v $(pwd):/app jekkos/composer composer install
   - docker run --rm -v $(pwd):/app jekkos/composer php bin/install.php translations develop
   - sed -i "s/'\(dev\)'/'$rev'/g" application/config/config.php