Prepare for the 2.11 dev SDKs (#35)

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 31cad3a..695c317 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,7 @@
 * Added `getRange(start, end)` and `characterAt(pos)` to `Characters`
   as alternative to `.take(end).skip(start)` and `getRange(pos, pos + 1)`.
 * Change some positional parameter names from `other` to `characters`.
+* Allow the 2.10 stable SDK.
 
 ## 1.1.0-nullsafety.2
 
diff --git a/pubspec.yaml b/pubspec.yaml
index e4fbb25..f5cd6da 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -5,10 +5,10 @@
 
 environment:
   # This must remain a tight constraint until nnbd is stable
-  sdk: '>=2.10.0-110 <2.10.0'
+  sdk: '>=2.10.0-110 <2.11.0'
 
 dev_dependencies:
-  test: "^1.6.0"
+  test: ^1.6.0
   pedantic: ^1.9.0
 
 dependency_overrides: