Raising minimum SDK constraint.
diff --git a/pubspec.yaml b/pubspec.yaml
index 613744d..b28993f 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -7,7 +7,7 @@
 homepage: https://github.com/dart-lang/dart_style
 
 environment:
-  sdk: '>=2.7.0 <3.0.0'
+  sdk: '>=2.9.0 <3.0.0'
 
 dependencies:
   analyzer: ^0.40.0