update SDK constraint for null safety
diff --git a/pubspec.yaml b/pubspec.yaml
index d2f5bcb..8ee0fe2 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -5,7 +5,7 @@
 homepage: https://github.com/google/vector_math.dart
 
 environment:
-  sdk: '>=2.3.0 <3.0.0'
+  sdk: '>=2.9.0-1 <3.0.0'
 
 dev_dependencies:
   benchmark_harness: any