NATS 1.2.x support: catch not set fields

This commit improves support for NATS 1.2.x by checking if several
fields; `auth_required`, `tls_required`, and `tls_verify` are set in
the initial INFO packet. As of NATS 1.2, these fields aren't always
set, which can cause an E_NOTICE to be raised.

Without this change, the unit tests are failing because the Docker
container has been updated to 1.2.0, and PHPUnit is configured to
treat notices as test failures.

See: nats-io/nats-server@17fecd4#diff-91bbeda7eb98a7adc57b9e47e2cf5c2b

Author: Mark Dain

src/Nats/ServerInfo.php

@@ -102,9 +102,9 @@ public function __construct($connectionResponse)
         $this->setPort($data['port']);
         $this->setVersion($data['version']);
         $this->setGoVersion($data['go']);
-        $this->setAuthRequired($data['auth_required']);
-        $this->setTLSRequired($data['tls_required']);
-        $this->setTLSVerify($data['tls_verify']);
+        $this->setAuthRequired(isset($data['auth_required']) ? $data['auth_required'] : false);
+        $this->setTLSRequired(isset($data['tls_required']) ? $data['tls_required'] : false);
+        $this->setTLSVerify(isset($data['tls_verify']) ? $data['tls_verify'] : false);
         $this->setMaxPayload($data['max_payload']);
 
         if (version_compare($data['version'], '1.1.0') === -1) {