Prepare for the 2.11 dev SDKs (#154)

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 04fbdff..1be3d5a 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,6 @@
-## 1.15.0-nullsafety.3-dev
+## 1.15.0-nullsafety.3
 
+* Allow 2.10 stable and 2.11.0 dev SDK versions.
 * Add `toUnorderedList` method on `PriorityQueue`.
 * Make `HeapPriorityQueue`'s `remove` and `contains` methods
   use `==` for equality checks.
diff --git a/pubspec.yaml b/pubspec.yaml
index 113b39b..d1baef6 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,11 +1,11 @@
 name: collection
-version: 1.15.0-nullsafety.3-dev
+version: 1.15.0-nullsafety.3
 
 description: Collections and utilities functions and classes related to collections.
 homepage: https://www.github.com/dart-lang/collection
 
 environment:
-  sdk: '>=2.10.0-78 <2.10.0'
+  sdk: '>=2.10.0-78 <2.11.0'
 
 dev_dependencies:
   pedantic: ^1.0.0