Bump drush version

Author: webflo

composer.json

@@ -21,7 +21,7 @@
  "drupal-composer/drupal-scaffold": "^2.2",
  "drupal/console": "^1.0.2",
  "drupal/core": "~8.4",
- "drush/drush": "~8.0|^9.0.0-beta8",
+ "drush/drush": "^9.0.0",
  "webflo/drupal-finder": "^1.0.0",
  "webmozart/path-util": "^2.3"
  },