Bugfix: Use server timestamp to set agent_last_seen_at (#1114)

db/migrate/20200802170002_reset_agent_last_seen_at.rb

@@ -0,0 +1,7 @@
+class ResetAgentLastSeenAt < ActiveRecord::Migration[6.0]
+  def change
+    # rubocop:disable Rails/SkipsModelValidations
+    ::Conversation.where('agent_last_seen_at > ?', DateTime.now.utc).update_all(agent_last_seen_at: DateTime.now.utc)
+    # rubocop:enable Rails/SkipsModelValidations
+  end
+end