Prepare for the 2.11 dev SDKs (dart-lang/pool#43)

Bump the upper bound to allow 2.10 stable and 2.11.0 dev SDK versions.
diff --git a/pkgs/pool/CHANGELOG.md b/pkgs/pool/CHANGELOG.md
index a413d78..5d9f6c4 100644
--- a/pkgs/pool/CHANGELOG.md
+++ b/pkgs/pool/CHANGELOG.md
@@ -1,3 +1,7 @@
+## 1.5.0-nullsafety.1
+
+* Allow 2.10 stable and 2.11.0 dev SDK versions.
+
 ## 1.5.0-nullsafety
 
 * Migrate to null safety.
diff --git a/pkgs/pool/pubspec.yaml b/pkgs/pool/pubspec.yaml
index abc21b5..68b7bb1 100644
--- a/pkgs/pool/pubspec.yaml
+++ b/pkgs/pool/pubspec.yaml
@@ -1,5 +1,5 @@
 name: pool
-version: 1.5.0-nullsafety
+version: 1.5.0-nullsafety.1
 
 description: >-
   Manage a finite pool of resources.
@@ -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'
 
 dependencies:
   async: '>=2.5.0-nullsafety <2.5.0'