Improve TLS handling

[clue]

PHP 5.6+ defaults to actually verifying the peer. The underlying SecureConnector does not currently pass the actual host name though:

https://travis-ci.org/clue/php-socks-react/jobs/71694378

[clue]

Also make sure to add PHP 5.6 to the test matrix.

[clue]

Will be resolved via reactphp-legacy/socket-client#43