Add missing stage_file_proxy

composer.json

@@ -69,6 +69,7 @@
         "drupal/sitemap": "^2.0",
         "drupal/smart_date": "^3.1",
         "drupal/smtp": "^1.0",
+        "drupal/stage_file_proxy": "^1.1",
         "drupal/subpathauto": "^1.1",
         "drupal/token": "^1.7",
         "drupal/unlimited_number": "^2.0",