test another checkout command

.travis.yml

@@ -26,7 +26,7 @@ script:
   # Run PHPUnit tests
   - docker exec -it tripal3 bash -c "cd /modules/tripal && composer install && DRUPAL_ROOT=/var/www/html ./vendor/bin/phpunit"
   # Test Tripal 2 installation
-  - git checkout -b 7.x-2.x origin/7.x-2.x
+  - git checkout refs/remotes/origin/7.x-2.x
   - docker run -it -d --rm --name tripal2 -v "$(pwd)":/modules/tripal statonlab/drupal7
   - sleep 10
   - docker exec -it tripal2 drush en -y tripal tripal_chado tripal_views