Replace deprecated JSON with json from dart:convert (dart-lang/yaml#48)

pkgs/yaml/README.md

diff --git a/pkgs/yaml/README.md b/pkgs/yaml/README.md
index 6f77bcd..93a7909 100644
--- a/pkgs/yaml/README.md
+++ b/pkgs/yaml/README.md
@@ -15,7 +15,7 @@
 ```
 
 This library currently doesn't support dumping to YAML. You should use
-`JSON.encode` from `dart:convert` instead:
+`json.encode` from `dart:convert` instead:
 
 ```dart
 import 'dart:convert';
@@ -23,6 +23,6 @@
 
 main() {
   var doc = loadYaml("YAML: YAML Ain't Markup Language");
-  print(JSON.encode(doc));
+  print(json.encode(doc));
 }
 ```