Update README.md (dart-lang/yaml#32)

pkgs/yaml/README.md

diff --git a/pkgs/yaml/README.md b/pkgs/yaml/README.md
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 A parser for [YAML](http://www.yaml.org/).
 
+[![Build Status](https://travis-ci.org/dart-lang/yaml.svg?branch=master)](https://travis-ci.org/dart-lang/yaml)
+
 Use `loadYaml` to load a single document, or `loadYamlStream` to load a
 stream of documents. For example: