Require drupal extension

This package is required as drupal extension is needed to detect the
context.

It is required any version as DrupalSubcontextBase have not changed
among versions

composer.json

@@ -12,6 +12,9 @@
     }
   ],
   "homepage": "https://www.drupal.org/project/behat_javascript",
+  "require": {
+    "drupal/drupal-extension": "*"
+  },
   "support": {
     "issues": "https://www.drupal.org/project/issues/behat_javascript"
   },