Update minimum supported Dart SDK

Ensures tests can be run
diff --git a/.travis.yml b/.travis.yml
index d412cc2..17ebd9e 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -3,7 +3,7 @@
 dart:
   - dev
   - stable
-  - 1.22.1
+  - 1.23.0
 
 dart_task:
   - test: --platform vm
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 94efabe..2211082 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,7 @@
+## 0.7.1
+
+* Update minimum Dart SDK to 1.23.0.
+
 ## 0.7.0
 
 * Give a return type to the `Handler` typedef. This may cause static warnings
diff --git a/pubspec.yaml b/pubspec.yaml
index c85e008..8c13155 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -4,7 +4,7 @@
 description: Web Server Middleware for Dart
 homepage: https://github.com/dart-lang/shelf
 environment:
-  sdk: '>=1.22.0 <2.0.0-dev.infinity'
+  sdk: '>=1.23.0 <2.0.0-dev.infinity'
 dependencies:
   async: '>=1.10.0 <3.0.0'
   collection: '^1.5.0'