Laravel 5.6 updates

Travis config update

Removed HHVM script as Laravel no longer support HHVM after releasing 5.3

vendor/phar-io/version/src/constraints/AbstractVersionConstraint.php

@@ -0,0 +1,32 @@
+<?php
+/*
+ * This file is part of PharIo\Version.
+ *
+ * (c) Arne Blankerts <arne@blankerts.de>, Sebastian Heuer <sebastian@phpeople.de>, Sebastian Bergmann <sebastian@phpunit.de>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace PharIo\Version;
+
+abstract class AbstractVersionConstraint implements VersionConstraint {
+    /**
+     * @var string
+     */
+    private $originalValue = '';
+
+    /**
+     * @param string $originalValue
+     */
+    public function __construct($originalValue) {
+        $this->originalValue = $originalValue;
+    }
+
+    /**
+     * @return string
+     */
+    public function asString() {
+        return $this->originalValue;
+    }
+}