Dart format with latest SDK (#56)

* Dart format with latest SDK

* only check format on dev sdk
diff --git a/.github/workflows/test-package.yml b/.github/workflows/test-package.yml
index 02921f3..f9a4bb3 100644
--- a/.github/workflows/test-package.yml
+++ b/.github/workflows/test-package.yml
@@ -31,7 +31,7 @@
         run: dart pub get
       - name: Check formatting
         run: dart format --output=none --set-exit-if-changed .
-        if: always() && steps.install.outcome == 'success'
+        if: matrix.sdk == 'dev' && steps.install.outcome == 'success'
       - name: Analyze code
         run: dart analyze --fatal-infos
         if: always() && steps.install.outcome == 'success'
diff --git a/lib/src/characters_impl.dart b/lib/src/characters_impl.dart
index 63140c8..a87aa68 100644
--- a/lib/src/characters_impl.dart
+++ b/lib/src/characters_impl.dart
@@ -1022,11 +1022,15 @@
   var index = 0;
   var replacement = outerReplacement;
   while ((index = breaks.nextBreak()) >= 0) {
-    buffer..write(replacement)..write(string.substring(start, index));
+    buffer
+      ..write(replacement)
+      ..write(string.substring(start, index));
     start = index;
     replacement = internalReplacement;
   }
-  buffer..write(outerReplacement)..write(string.substring(end));
+  buffer
+    ..write(outerReplacement)
+    ..write(string.substring(end));
   return buffer.toString();
 }