Update pubspec.yaml (#24)

diff --git a/pkgs/unified_analytics/pubspec.yaml b/pkgs/unified_analytics/pubspec.yaml
index edcc725..a3c9ddc 100644
--- a/pkgs/unified_analytics/pubspec.yaml
+++ b/pkgs/unified_analytics/pubspec.yaml
@@ -8,7 +8,7 @@
 repository: https://github.com/dart-lang/tools/tree/main/pkgs/unified_analytics
 
 environment:
-  sdk: '>=2.19.0 <3.0.0'
+  sdk: '>=2.19.0 <4.0.0'
 
 dependencies:
   clock: ^1.1.1