Update thoughtbot logo

Author: tysongach

README.md

@@ -690,7 +690,7 @@ Jackson][rondale-sc].
 [rondale-sc]: https://github.com/rondale-sc
 [seanpdoyle]: https://github.com/seanpdoyle
 
-![thoughtbot](https://thoughtbot.com/logo.png)
+![thoughtbot](http://presskit.thoughtbot.com/images/thoughtbot-logo-for-readmes.svg)
 
 ember-cli-rails is maintained and funded by thoughtbot, inc.
 The names and logos for thoughtbot are trademarks of thoughtbot, inc.