Laravel 5.6 updates

Travis config update

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

vendor/symfony/http-kernel/Tests/CacheClearer/Psr6CacheClearerTest.php

@@ -45,25 +45,4 @@ class Psr6CacheClearerTest extends TestCase
     {
         (new Psr6CacheClearer())->clearPool('unknown');
     }
-
-    /**
-     * @group legacy
-     * @expectedDeprecation The Symfony\Component\HttpKernel\CacheClearer\Psr6CacheClearer::addPool() method is deprecated since Symfony 3.3 and will be removed in 4.0. Pass an array of pools indexed by name to the constructor instead.
-     */
-    public function testClearPoolsInjectedByAdder()
-    {
-        $pool1 = $this->getMockBuilder(CacheItemPoolInterface::class)->getMock();
-        $pool1
-            ->expects($this->once())
-            ->method('clear');
-
-        $pool2 = $this->getMockBuilder(CacheItemPoolInterface::class)->getMock();
-        $pool2
-            ->expects($this->once())
-            ->method('clear');
-
-        $clearer = new Psr6CacheClearer(array('pool1' => $pool1));
-        $clearer->addPool($pool2);
-        $clearer->clear('');
-    }
 }