misc: fix dependency on fake_async (#8)

diff --git a/pubspec.yaml b/pubspec.yaml
index d9261a7..ab20de2 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -13,5 +13,5 @@
   http: ^0.11.0
 
 dev_dependencies:
-  fake_async: ^0.1.2
+  fake_async: ^1.0.0
   test: ^1.2.0