change docker client sdk version

vendor/github.com/docker/libtrust/CONTRIBUTING.md

@@ -0,0 +1,13 @@
+# Contributing to libtrust
+
+Want to hack on libtrust? Awesome! Here are instructions to get you
+started.
+
+libtrust is a part of the [Docker](https://www.docker.com) project, and follows
+the same rules and principles. If you're already familiar with the way
+Docker does things, you'll feel right at home.
+
+Otherwise, go read
+[Docker's contributions guidelines](https://github.com/docker/docker/blob/master/CONTRIBUTING.md).
+
+Happy hacking!