removed unused dart:async (#608)

diff --git a/lib/services_gae.dart b/lib/services_gae.dart
index 1cc7e1c..44e6311 100644
--- a/lib/services_gae.dart
+++ b/lib/services_gae.dart
@@ -4,7 +4,6 @@
 
 library services_gae;
 
-import 'dart:async';
 import 'dart:io' as io;
 import 'dart:math';