try again to fix xxe test

Author: gggeek

tests/04ParsingTest.php

@@ -728,7 +728,7 @@ public function testXXE()
         $req = new \PhpXmlRpc\Request('hi');
         $resp = $req->parseResponse($xml, true);
         $val = $resp->value();
-        if (version_compare(PHP_VERSION, '7.0.0', '>=')) {
+        if (version_compare(PHP_VERSION, '5.6.0', '>=')) {
             $this->assertequals('', $val->scalarVal());
         } else {
             $this->assertequals('&xxe;', $val->scalarVal());