Laravel 5.6 updates

Travis config update

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

vendor/dragonmantank/cron-expression/src/Cron/FieldInterface.php

@@ -0,0 +1,40 @@
+<?php
+
+namespace Cron;
+use DateTime;
+
+/**
+ * CRON field interface
+ */
+interface FieldInterface
+{
+    /**
+     * Check if the respective value of a DateTime field satisfies a CRON exp
+     *
+     * @param DateTime $date  DateTime object to check
+     * @param string   $value CRON expression to test against
+     *
+     * @return bool Returns TRUE if satisfied, FALSE otherwise
+     */
+    public function isSatisfiedBy(DateTime $date, $value);
+
+    /**
+     * When a CRON expression is not satisfied, this method is used to increment
+     * or decrement a DateTime object by the unit of the cron field
+     *
+     * @param DateTime $date   DateTime object to change
+     * @param bool     $invert (optional) Set to TRUE to decrement
+     *
+     * @return FieldInterface
+     */
+    public function increment(DateTime $date, $invert = false);
+
+    /**
+     * Validates a CRON expression for a given field
+     *
+     * @param string $value CRON expression value to validate
+     *
+     * @return bool Returns TRUE if valid, FALSE otherwise
+     */
+    public function validate($value);
+}