Add HHVM 3.4+ badge - this library's tests are all passing on HHVM:) [ci skip]

Author: thekid

README.md

@@ -5,6 +5,7 @@ FTP protocol support for the XP Framework
 [![XP Framework Module](https://raw.githubusercontent.com/xp-framework/web/master/static/xp-framework-badge.png)](https://github.com/xp-framework/core)
 [![BSD Licence](https://raw.githubusercontent.com/xp-framework/web/master/static/licence-bsd.png)](https://github.com/xp-framework/core/blob/master/LICENCE.md)
 [![Required PHP 5.4+](https://raw.githubusercontent.com/xp-framework/web/master/static/php-5_4plus.png)](http://php.net/)
+[![Required HHVM 3.4+](https://raw.githubusercontent.com/xp-framework/web/master/static/hhvm-3_4plus.png)](http://hhvm.com/)
 [![Latest Stable Version](https://poser.pugx.org/xp-framework/ftp/version.png)](https://packagist.org/packages/xp-framework/ftp)
 
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