Add travis-ci badge to README.

Author: N. Taylor Mullen

README.md

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 Razor Tooling
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+Travis:   [![Travis](https://travis-ci.org/aspnet/RazorTooling.svg?branch=dev)](https://travis-ci.org/aspnet/RazorTooling)
+
 The Razor syntax provide a fast, terse, clean and lightweight way to combine server code with HTML to create dynamic web content. This repo contains tooling that interacts with the DNX Design Time Host to provide a Razor editing experience.
 
 This project is part of ASP.NET 5. You can find samples, documentation and getting started instructions for ASP.NET 5 at the [Home](https://www.github.com/aspnet/home) repo.