bump SDK constraint for 2.11 (#170)

diff --git a/packages/file/pubspec.yaml b/packages/file/pubspec.yaml
index d7e94c8..cb18e79 100644
--- a/packages/file/pubspec.yaml
+++ b/packages/file/pubspec.yaml
@@ -7,7 +7,7 @@
 homepage: https://github.com/google/file.dart
 
 environment:
-  sdk: '>=2.10.0-4.0.dev <2.10.0'
+  sdk: '>=2.10.0-0.0 <2.11.0'
 
 dependencies:
   meta: ^1.3.0-nullsafety.2