[travis-ci] Fix composer install
[travis-ci] Fix composer install

Bug introduced in fa83f08a6e61896b594395f618f8ee1e4807005f

matbech/zend-mail,Xerkus/zend-mail,MadCat34/zend-mail,basz/zend-mail,mleko/zend-mail,rapidsoft-de/zend-mail,stefanotorresi/zend-mail