update SDK constraint for null safety (#172)

diff --git a/packages/file/CHANGELOG.md b/packages/file/CHANGELOG.md
index 4f83155..feada17 100644
--- a/packages/file/CHANGELOG.md
+++ b/packages/file/CHANGELOG.md
@@ -1,3 +1,7 @@
+#### 6.0.0-nullsafety.3
+
+* Update upper bound of SDK constraint.
+
 #### 6.0.0-nullsafety.2
 
 * Make `ForwardingFile.openRead`'s return type again match the return type from
diff --git a/packages/file/pubspec.yaml b/packages/file/pubspec.yaml
index cb18e79..6d20a67 100644
--- a/packages/file/pubspec.yaml
+++ b/packages/file/pubspec.yaml
@@ -1,5 +1,5 @@
 name: file
-version: 6.0.0-nullsafety.2
+version: 6.0.0-nullsafety.3
 description:
   A pluggable, mockable file system abstraction for Dart. Supports local file
   system access, as well as in-memory file systems, record-replay file systems,
@@ -7,12 +7,12 @@
 homepage: https://github.com/google/file.dart
 
 environment:
-  sdk: '>=2.10.0-0.0 <2.11.0'
+  sdk: '>=2.10.0-0.0 <2.12.0'
 
 dependencies:
   meta: ^1.3.0-nullsafety.2
   path: ^1.8.0-nullsafety
 
 dev_dependencies:
-  test: '^1.16.0-nullsafety.1'
   file_testing: '>=2.0.0 <3.0.0'
+  test: '^1.16.0-nullsafety.1'