Collapse -nullsafety version CHANGELOG (#575)

Author: natebosch

CHANGELOG.md

@@ -1,3 +1,5 @@
+## 0.13.4-dev
+
 ## 0.13.3
 
 * Validate that the `method` parameter of BaseRequest is a valid "token".
@@ -13,10 +15,6 @@
 
 ## 0.13.0
 
-* Stable null safety release.
-
-## 0.13.0-nullsafety.0
-
 * Migrate to null safety.
 * Add `const` constructor to `ByteStream`.
 * Migrate `BrowserClient` from `blob` to `arraybuffer`.

pubspec.yaml

@@ -1,5 +1,5 @@
 name: http
-version: 0.13.3
+version: 0.13.4-dev
 homepage: https://github.com/dart-lang/http
 description: A composable, multi-platform, Future-based API for HTTP requests.