Prepare for the 2.11 dev SDKs (#23)

Bump the upper bound to allow 2.10 stable and 2.11.0 dev SDK versions.
diff --git a/CHANGELOG.md b/CHANGELOG.md
index bce195f..935b5cc 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,7 @@
+## 1.1.0-nullsafety.1
+
+* Allow 2.10 stable and 2.11.0 dev SDK versions.
+
 ## 1.1.0-nullsafety
 
 * Update to null safety.
diff --git a/pubspec.yaml b/pubspec.yaml
index e6391b3..5904b67 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,11 +1,11 @@
 name: clock
-version: 1.1.0-nullsafety
+version: 1.1.0-nullsafety.1
 description: A fakeable wrapper for dart:core clock APIs
 homepage: https://github.com/dart-lang/clock
 
 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: ^1.0.0