update versions for beta (#173)

diff --git a/packages/file/CHANGELOG.md b/packages/file/CHANGELOG.md
index feada17..62bc35f 100644
--- a/packages/file/CHANGELOG.md
+++ b/packages/file/CHANGELOG.md
@@ -1,3 +1,7 @@
+#### 6.0.0-nullsafety.4
+
+* Update upper bound of SDK constraint.
+
 #### 6.0.0-nullsafety.3
 
 * Update upper bound of SDK constraint.
diff --git a/packages/file/pubspec.yaml b/packages/file/pubspec.yaml
index 6d20a67..435c714 100644
--- a/packages/file/pubspec.yaml
+++ b/packages/file/pubspec.yaml
@@ -1,5 +1,5 @@
 name: file
-version: 6.0.0-nullsafety.3
+version: 6.0.0-nullsafety.4
 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 <2.12.0'
+  sdk: '>=2.12.0-0 <3.0.0'
 
 dependencies:
-  meta: ^1.3.0-nullsafety.2
-  path: ^1.8.0-nullsafety
+  meta: ^1.3.0-nullsafety.6
+  path: ^1.8.0-nullsafety.3
 
 dev_dependencies:
   file_testing: '>=2.0.0 <3.0.0'
-  test: '^1.16.0-nullsafety.1'
+  test: '^1.16.0-nullsafety.8'