Laravel 5.6 updates

Travis config update

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

vendor/sebastian/diff/tests/Utils/FileUtils.php

@@ -0,0 +1,31 @@
+<?php declare(strict_types=1);
+/*
+ * This file is part of sebastian/diff.
+ *
+ * (c) 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 SebastianBergmann\Diff\Utils;
+
+final class FileUtils
+{
+    public static function getFileContent(string $file): string
+    {
+        $content = @\file_get_contents($file);
+
+        if (false === $content) {
+            $error = \error_get_last();
+
+            throw new \RuntimeException(\sprintf(
+                'Failed to read content of file "%s".%s',
+                $file,
+                $error ? ' ' . $error['message'] : ''
+            ));
+        }
+
+        return $content;
+    }
+}