Update sdk constraint to enable NNBD strong mode
diff --git a/pubspec.yaml b/pubspec.yaml
index de57297..25a3aeb 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -4,7 +4,7 @@
 description: Utilities for working with Foreign Function Interface (FFI) code.
 
 environment:
-  sdk: '>=2.6.0 <3.0.0'
+  sdk: '>=2.9.0 <3.0.0'
 
 # dependencies: