prepare for stable release (dart-lang/io#71)

pkgs/io/CHANGELOG.md

diff --git a/pkgs/io/CHANGELOG.md b/pkgs/io/CHANGELOG.md
index 727feee..9fdad92 100644
--- a/pkgs/io/CHANGELOG.md
+++ b/pkgs/io/CHANGELOG.md
@@ -1,4 +1,4 @@
-## 0.4.0
+## 1.0.0
 
 * Migrate this package to null-safety
 * Require Dart >=2.12

pkgs/io/pubspec.yaml

diff --git a/pkgs/io/pubspec.yaml b/pkgs/io/pubspec.yaml
index 1a39c95..3410339 100644
--- a/pkgs/io/pubspec.yaml
+++ b/pkgs/io/pubspec.yaml
@@ -2,7 +2,7 @@
 description: >-
   Utilities for the Dart VM Runtime including support for ANSI colors,
   file copying, and standard exit code values.
-version: 0.4.0-dev
+version: 1.0.0
 repository: https://github.com/dart-lang/io
 
 environment: