Prepare for the 2.11 dev SDKs (flutter#16)

Bump the upper bound to allow 2.10 stable and 2.11.0 dev SDK versions.

Author: natebosch

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.

pubspec.yaml

@@ -1,13 +1,13 @@
 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.
 homepage: https://github.com/dart-lang/charcode
 
 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