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 c4926bd..f5c7ed2 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
 
 * Update to null safety. All apis require non-nullable types.
diff --git a/pubspec.yaml b/pubspec.yaml
index f69546d..5027d8e 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,12 +1,12 @@
 name: term_glyph
-version: 1.2.0-nullsafety
+version: 1.2.0-nullsafety.1
 
 description: Useful Unicode glyphs and ASCII substitutes.
 homepage: https://github.com/dart-lang/term_glyph
 
 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:
   csv: '>=3.0.0 <5.0.0'