Update README.md

Author: IainNZ

README.md

@@ -2,7 +2,7 @@
 
 This package offers Python-style general formatting and c-style numerical formatting (for speed).
 
-[![Build Status](https://travis-ci.org/JuliaLang/Formatting.jl.png?branch=master)](https://travis-ci.org/JuliaLang/Formatting.jl)
+[![Build Status](https://travis-ci.org/JuliaLang/Formatting.jl.svg?branch=master)](https://travis-ci.org/JuliaLang/Formatting.jl)
 [![Formatting](http://pkg.julialang.org/badges/Formatting_0.3.svg)](http://pkg.julialang.org/?pkg=Formatting&ver=0.3)
 [![Formatting](http://pkg.julialang.org/badges/Formatting_0.4.svg)](http://pkg.julialang.org/?pkg=Formatting&ver=0.4)