Feature / Fix: Update SocketClient to v0.5 and fix secure connection via TLS (#38 by @clue)

Improve test suite by adding PHPUnit to require-dev, fix HHVM build for now again and ignore future HHVM build errors, test against legacy PHP 5.3 through PHP 7.1 and lock Travis distro so new defaults will not break the build (#34, #35, #36 and #37 by @clue)