add travis badge to README

Author: Tom Schlick

README.md

@@ -1,3 +1,6 @@
-# laravel-http2-server-push
+# Laravel HTTP/2 Server Push Middleware
+
+[![Build Status](https://travis-ci.org/tomschlick/laravel-http2-server-push.svg?branch=master)](https://travis-ci.org/tomschlick/laravel-http2-server-push)
+
 
 A middleware package for Laravel 5 to enable server push for your script, style, and image assets.