chore: regens API reference docs (#889)

diff --git a/docs/dyn/pubsub_v1.projects.topics.subscriptions.html b/docs/dyn/pubsub_v1.projects.topics.subscriptions.html
index 22b40f6..a1da8d5 100644
--- a/docs/dyn/pubsub_v1.projects.topics.subscriptions.html
+++ b/docs/dyn/pubsub_v1.projects.topics.subscriptions.html
@@ -86,7 +86,7 @@
   <pre>Lists the names of the subscriptions on this topic.
 
 Args:
-  topic: string, The name of the topic that subscriptions are attached to.
+  topic: string, Required. The name of the topic that subscriptions are attached to.
 Format is `projects/{project}/topics/{topic}`. (required)
   pageSize: integer, Maximum number of subscription names to return.
   pageToken: string, The value returned by the last `ListTopicSubscriptionsResponse`; indicates