Prepare to release 1.5.0-beta (#1787)

pkgs/http/CHANGELOG.md

diff --git a/pkgs/http/CHANGELOG.md b/pkgs/http/CHANGELOG.md
index ee8bfa7..d29dfc2 100644
--- a/pkgs/http/CHANGELOG.md
+++ b/pkgs/http/CHANGELOG.md
@@ -1,4 +1,4 @@
-## 1.5.0-wip
+## 1.5.0-beta
 
 * Added support for aborting requests before they complete.
 * Clarify that some header names may not be sent/received.

pkgs/http/pubspec.yaml

diff --git a/pkgs/http/pubspec.yaml b/pkgs/http/pubspec.yaml
index 2c8eafc..e243e5f 100644
--- a/pkgs/http/pubspec.yaml
+++ b/pkgs/http/pubspec.yaml
@@ -1,5 +1,5 @@
 name: http
-version: 1.5.0-wip
+version: 1.5.0-beta
 description: A composable, multi-platform, Future-based API for HTTP requests.
 repository: https://github.com/dart-lang/http/tree/master/pkgs/http