fixes the hardcoded protocol class in the server

jetforce/server.py

@@ -103,7 +103,7 @@ class GeminiServer(Factory):
         It builds the instance of the protocol class, which is what actually
         implements the Gemini protocol.
         """
-        return GeminiProtocol(self, self.app)
+        return self.__class__.protocol_class(self, self.app)
 
     def initialize(self) -> None:
         """