Update client.rb (#5)

Fix typo in variable name

Co-authored-by: David Christensen <david@endpoint.com>

Author: machack666

lib/zulip/client.rb

@@ -64,7 +64,7 @@ def register(event_types: [], narrow: [])
         res = JSON.parse(response.body, symbolize_names: true)
         [res[:queue_id], res[:last_event_id]]
       else
-        raise Zulip::ResponseError, reqponse.reason_phrase
+        raise Zulip::ResponseError, response.reason_phrase
       end
     end