Allow the 2.10 stable and 2.11.0 dev SDKs (#15)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index d818c7e..2c719a3 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,4 +1,4 @@
-## v0.3.0
+## v0.3.0-nullsafety-dev
 
 * The `SyncHttpClientResponse.contentLength` getter will return `-1` instead of
   `null` if content length not specified.
diff --git a/pubspec.yaml b/pubspec.yaml
index ad78f6e..2c27943 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,5 +1,5 @@
 name: sync_http
-version: 0.3.0-dev
+version: 0.3.0-nullsafety-dev
 description: Synchronous HTTP client for Dart.
 homepage: https://github.com/dart-lang/sync_http
 
@@ -8,7 +8,7 @@
 
 environment:
   # This must remain a tight constraint until nnbd is stable.
-  sdk: '>=2.10.0-0 <2.10.0'
+  sdk: '>=2.10.0-0 <2.11.0'
 
 dev_dependencies:
   test: ^1.2.0