Prepare for the 2.11 dev SDKs (#16)

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 7f3fc36..6941772 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,7 @@
+## 1.2.0-nullsafety.1
+
+- Allow 2.10 stable and 2.11.0 dev SDK versions.
+
 ## 1.2.0-nullsafety
 
 - Opt in to null safety.
diff --git a/pubspec.yaml b/pubspec.yaml
index dffa427..396897e 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,5 +1,5 @@
 name: charcode
-version: 1.2.0-nullsafety
+version: 1.2.0-nullsafety.1
 description: >-
   Constants for ASCII and common non-ASCII character codes represented by
   top-level constants.
@@ -7,7 +7,7 @@
 
 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:
   pedantic: ^1.0.0