pkg/csslib: remove drone.io reference from README

R=jmesserly@google.com

Review URL: https://codereview.chromium.org//62913002

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart/pkg/csslib@29992 260f80e4-7a28-3924-810f-c04153c831b5
diff --git a/README.md b/README.md
index b84dae4..e64fd9b 100644
--- a/README.md
+++ b/README.md
@@ -4,8 +4,6 @@
 This is a pure [Dart][dart] [CSS parser][cssparse]. Since it's 100%
 Dart you can use it safely from a script or server side app.
 
-[![Build Status](https://drone.io/github.com/dart-lang/csslib/status.png)](https://drone.io/github.com/dart-lang/csslib/latest)
-
 Installation
 ------------