[travis/php-5.5] Also build on PHP 5.5 environment.
[travis/php-5.5] Also build on PHP 5.5 environment.

ericariyanto/phpseclib,paragonie-scott/phpseclib,melya/phpseclib,kenichiii/phpseclib,splitice/phpseclib,melya/phpseclib,creatuity/phpseclib,phpseclib/phpseclib-php5,ericariyanto/phpseclib,phpseclib/phpseclib-php5,kenichiii/phpseclib,metaclassing/phpseclib,phpseclib/phpseclib,danog/phpseclib,splitice/phpseclib,creatuity/phpseclib,thaigialai1987/phpseclib,metaclassing/phpseclib,terrafrost/phpseclib,danog/phpseclib,thaigialai1987/phpseclib,paragonie-scott/phpseclib