Maintain default delimiter of newline

With the addition of the delimiter interface users can now override the
delimiter in the stream. With this additional interface we want to
maintain compatibility-- namely we want to continue using a newline in
the event that the marshaler doesn't implement the new interface (for
backwards compatibility).

Fixes #495

runtime/handler.go

@@ -41,6 +41,8 @@ func ForwardResponseStream(ctx context.Context, mux *ServeMux, marshaler Marshal
 	var delimiter []byte
 	if d, ok := marshaler.(Delimited); ok {
 		delimiter = d.Delimiter()
+	} else {
+	    delimiter = []byte("\n")
 	}
 
 	var wroteHeader bool