Update travis badge [skip ci]

I know this is a bit lame, but the svg badge does look better =)

Author: arthurnn

README.md

@@ -1,6 +1,6 @@
 ![Elixir](https://github.com/elixir-lang/elixir-lang.github.com/raw/master/images/logo/logo.png)
 =========
-[![Build Status](https://secure.travis-ci.org/elixir-lang/elixir.png?branch=master "Build Status")](http://travis-ci.org/elixir-lang/elixir)
+[![Build Status](https://secure.travis-ci.org/elixir-lang/elixir.svg?branch=master "Build Status")](http://travis-ci.org/elixir-lang/elixir)
 
 For more about Elixir, installation and documentation, [check Elixir's website](http://elixir-lang.org/).