Prepare to publish (#360)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index c87e445..482e722 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,4 +1,4 @@
-## 0.12.0+4-dev
+## 0.12.0+4
 
 * Fix a bug setting the `'content-type'` header in `MultipartRequest`.
 
diff --git a/pubspec.yaml b/pubspec.yaml
index f14a504..a44caff 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,5 +1,5 @@
 name: http
-version: 0.12.0+4-dev
+version: 0.12.0+4
 homepage: https://github.com/dart-lang/http
 description: A composable, multi-platform, Future-based API for HTTP requests.