Task #21: Updated drupal core version to beta1

Changed revision's hash as to fit Drupal 8.0.0-beta1 (http://cgit.drupalcode.org/drupal/commit/?id=64de978a08663904ba8231f20d2f26c8f5a135e8)
Merge pull request #22 from ccamara/master

Task #21: Updated drupal core version to beta1