Put back to composer. do that in part 2.

Author: martincollar

composer.json

@@ -57,6 +57,7 @@
         "drupal/seckit": "^2.0",
         "drupal/security_review": "1.x-dev",
         "drupal/shield": "^1.2",
+        "drupal/slack_invite": "^2.0",
         "drupal/stage_file_proxy": "^1.0@RC",
         "drupal/token": "^1.5",
         "drupal/upgrade_status": "^3.0@beta",