changed docstring spacing

sanic/app.py

@@ -123,11 +123,9 @@ class Sanic:
 
         Args:
             listener: callable i.e. setup_db(app, loop)
-
             event: when to register listener i.e. 'before_server_start'
 
         Returns: listener
-
         """
 
         return self.listener(event)(listener)