doc: add petkaantonov as collaborator

PR-URL: https://github.com/iojs/io.js/pull/1179
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: cjihrig <cjihrig@gmail.com>

README.md

@@ -285,6 +285,7 @@ information about the governance of the io.js project, see
 * **Julian Duque** ([@julianduque](https://github.com/julianduque)) <julianduquej@gmail.com>
 * **Johan Bergström** ([@jbergstroem](https://github.com/jbergstroem)) <bugs@bergstroem.nu>
 * **Roman Reiss** ([@silverwind](https://github.com/silverwind)) <me@silverwind.io>
+* **Petka Antonov** ([@petkaantonov](https://github.com/petkaanotnov)) <petka_antonov@hotmail.com>
 
 Collaborators follow the [COLLABORATOR_GUIDE.md](./COLLABORATOR_GUIDE.md) in
 maintaining the io.js project.