updates for the next version of package:yaml (dart-lang/yaml_edit#45)

diff --git a/pkgs/yaml_edit/CHANGELOG.md b/pkgs/yaml_edit/CHANGELOG.md
index 797a07f..cf1c47f 100644
--- a/pkgs/yaml_edit/CHANGELOG.md
+++ b/pkgs/yaml_edit/CHANGELOG.md
@@ -1,3 +1,7 @@
+## 2.1.1
+
+- Update to work with an unreleased version of `package:yaml`.
+
 ## 2.1.0
 - **Breaking** `wrapAsYamlNode(value, collectionStyle, scalarStyle)` will apply
   `collectionStyle` and `scalarStyle` recursively when wrapping a children of
diff --git a/pkgs/yaml_edit/lib/src/strings.dart b/pkgs/yaml_edit/lib/src/strings.dart
index 62fe280..f156afe 100644
--- a/pkgs/yaml_edit/lib/src/strings.dart
+++ b/pkgs/yaml_edit/lib/src/strings.dart
@@ -139,13 +139,14 @@
     assertValidScalar(value.value);
 
     if (value.value is String) {
-      if (_hasUnprintableCharacters(value.value) ||
+      final val = value.value as String;
+      if (_hasUnprintableCharacters(val) ||
           value.style == ScalarStyle.DOUBLE_QUOTED) {
-        return _yamlEncodeDoubleQuoted(value.value);
+        return _yamlEncodeDoubleQuoted(val);
       }
 
       if (value.style == ScalarStyle.SINGLE_QUOTED) {
-        return _tryYamlEncodeSingleQuoted(value.value);
+        return _tryYamlEncodeSingleQuoted(val);
       }
     }
 
@@ -172,23 +173,23 @@
     assertValidScalar(value.value);
 
     if (value.value is String) {
-      if (_hasUnprintableCharacters(value.value)) {
-        return _yamlEncodeDoubleQuoted(value.value);
+      final val = value.value as String;
+      if (_hasUnprintableCharacters(val)) {
+        return _yamlEncodeDoubleQuoted(val);
       }
 
       if (value.style == ScalarStyle.SINGLE_QUOTED) {
-        return _tryYamlEncodeSingleQuoted(value.value);
+        return _tryYamlEncodeSingleQuoted(val);
       }
 
       // Strings with only white spaces will cause a misparsing
-      if (value.value.trim().length == value.value.length &&
-          value.value.length != 0) {
+      if (val.trim().length == val.length && val.isNotEmpty) {
         if (value.style == ScalarStyle.FOLDED) {
-          return _tryYamlEncodeFolded(value.value, indentation, lineEnding);
+          return _tryYamlEncodeFolded(val, indentation, lineEnding);
         }
 
         if (value.style == ScalarStyle.LITERAL) {
-          return _tryYamlEncodeLiteral(value.value, indentation, lineEnding);
+          return _tryYamlEncodeLiteral(val, indentation, lineEnding);
         }
       }
     }
diff --git a/pkgs/yaml_edit/pubspec.yaml b/pkgs/yaml_edit/pubspec.yaml
index d726abe..8ddaafb 100644
--- a/pkgs/yaml_edit/pubspec.yaml
+++ b/pkgs/yaml_edit/pubspec.yaml
@@ -1,5 +1,5 @@
 name: yaml_edit
-version: 2.1.0
+version: 2.1.1
 description: A library for YAML manipulation with comment and whitespace preservation.
 repository: https://github.com/dart-lang/yaml_edit
 issue_tracker: https://github.com/dart-lang/yaml_edit/issues