Fix lack of override qualifier.

Author: evoskuil

include/bitcoin/node/protocols/protocol_explore.hpp

@@ -49,7 +49,7 @@ class BCN_API protocol_explore
 
 protected:
     void handle_receive_get(const code& ec,
-        const network::http::method::get& request) NOEXCEPT;
+        const network::http::method::get& request) NOEXCEPT override;
 };
 
 } // namespace node