Fix typo

src/brpc/controller.cpp

@@ -690,7 +690,7 @@ inline bool does_error_affect_main_socket(int error_code) {
         error_code == EINVAL/*returned by connect "0.0.0.1"*/;
 }
 
-//Note: A RPC call is probably consisted by serveral individual Calls such as
+//Note: A RPC call is probably consisted by several individual Calls such as
 //      retries and backup requests. This method simply cares about the error of
 //      this very Call (specified by |error_code|) rather than the error of the
 //      entire RPC (specified by c->FailedInline()).