Fix Travis for 7.x-1.x branch [2h]

[AronNovak]

Right now all builds fail:

$ cd $TRAVIS_BUILD_DIR/../drupal
before_script.2
0.18s$ git pull origin 7.x
From https://git.drupal.org/project/drupal
 * branch            7.x        -> FETCH_HEAD
Already up to date.
0.08s$ drush -v site-install minimal --db-url=mysql:https://root:@localhost/drupal --yes
The program 'drush' is currently not installed. To run 'drush' please ask your administrator to install the package 'drush'
The command "drush -v site-install minimal --db-url=mysql:https://root:@localhost/drupal --yes" failed and exited with 127 during .
Your build has been stopped.

https://travis-ci.org/RESTful-Drupal/restful/jobs/394923913