readme: fix build status badge

PR-URL: https://github.com/nodejs/http-parser/pull/277
Reviewed-By: Fedor Indutny <fedor@indutny.com>

README.md

@@ -1,7 +1,7 @@
 HTTP Parser
 ===========
 
-[![Build Status](https://travis-ci.org/joyent/http-parser.png?branch=master)](https://travis-ci.org/joyent/http-parser)
+[![Build Status](https://api.travis-ci.org/nodejs/http-parser.svg?branch=master)](https://travis-ci.org/nodejs/http-parser)
 
 This is a parser for HTTP messages written in C. It parses both requests and
 responses. The parser is designed to be used in performance HTTP