prepare to release 0.12.0 (#199)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index d084ff7..88e056b 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,4 +1,4 @@
-## 0.12.0-dev
+## 0.12.0
 
 ### New Features
 
diff --git a/pubspec.yaml b/pubspec.yaml
index 67730fe..887059e 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,5 +1,5 @@
 name: http
-version: 0.12.0-dev
+version: 0.12.0
 author: "Dart Team <misc@dartlang.org>"
 homepage: https://github.com/dart-lang/http
 description: A composable, Future-based API for making HTTP requests.