Update for beta release (#28)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 2980e25..7d6b6fb 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,7 @@
+### 3.0.0-nullsafety.4
+
+* Update supported SDK range.
+
 ### 3.0.0-nullsafety.3
 
 * Update supported SDK range.
diff --git a/pubspec.yaml b/pubspec.yaml
index 4b5d08f..484dd2d 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,10 +1,10 @@
 name: platform
-version: 3.0.0-nullsafety.3
+version: 3.0.0-nullsafety.4
 description: A pluggable, mockable platform abstraction for Dart.
 homepage: https://github.com/google/platform.dart
 
 environment:
-  sdk: '>=2.10.0-0.0 <2.12.0'
+  sdk: '>=2.12.0-0 <3.0.0'
 
 dev_dependencies:
   test: ^1.16.0-nullsafety.1