change metadata type

Signed-off-by: Vasiliy Tolstov <v.tolstov@unistack.org>

options.go

@@ -135,12 +135,10 @@ func RegisterRPCHandler(b bool) server.Option {
 
 type handlerMetadataKey struct{}
 
-func HandlerMetadata(md map[string]map[string]string) server.HandlerOption {
+func HandlerMetadata(md map[string]map[string]map[string]string) server.HandlerOption {
 	return server.SetHandlerOption(handlerMetadataKey{}, md)
 }
 
-type headerKey struct{}
-
 type handlerOptions struct {
 	headers []string
 	cookies []string