Support Dart 2.11 (#85)

diff --git a/pubspec.yaml b/pubspec.yaml
index 3cc2b21..867f8d3 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -11,7 +11,7 @@
 publish_to: none
 
 environment:
-  sdk: '>=2.10.0-0.0 <2.11.0'
+  sdk: '>=2.10.0-0.0 <2.12.0'
 
 dev_dependencies:
   pedantic: ^1.10.0-nullsafety