TravisCI: drop 5.3.3 due to compose errors on it
TravisCI: drop 5.3.3 due to compose errors on it

paragonie-scott/phpseclib,danog/phpseclib,terrafrost/phpseclib,metaclassing/phpseclib,paragonie-scott/phpseclib,phpseclib/phpseclib,metaclassing/phpseclib,danog/phpseclib