get ready for publish (#52)

diff --git a/pubspec.yaml b/pubspec.yaml
index 42c340b..658feb5 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,15 +1,15 @@
 name: process
-version: 4.0.0-nullsafety.3
+version: 4.0.0-nullsafety.4
 description: A pluggable, mockable process invocation abstraction for Dart.
 homepage: https://github.com/google/process.dart
 
 environment:
-  sdk: '>=2.10.0-0.0 <2.12.0'
+  sdk: '>=2.12.0-0 <3.0.0'
 
 dependencies:
-  file: '^6.0.0-nullsafety.1'
-  path: ^1.8.0-nullsafety
-  platform: '^3.0.0-nullsafety.1'
+  file: '^6.0.0-nullsafety.4'
+  path: ^1.8.0-nullsafety.3
+  platform: '^3.0.0-nullsafety.4'
 
 dev_dependencies:
-  test: ^1.16.0-nullsafety.1
+  test: ^1.16.0-nullsafety.8