Laravel 5.6 updates

Travis config update

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

vendor/symfony/http-foundation/HeaderBag.php

@@ -46,7 +46,7 @@ class HeaderBag implements \IteratorAggregate, \Countable
         $max = max(array_map('strlen', array_keys($headers))) + 1;
         $content = '';
         foreach ($headers as $name => $values) {
-            $name = implode('-', array_map('ucfirst', explode('-', $name)));
+            $name = ucwords($name, '-');
             foreach ($values as $value) {
                 $content .= sprintf("%-{$max}s %s\r\n", $name.':', $value);
             }
@@ -294,21 +294,9 @@ class HeaderBag implements \IteratorAggregate, \Countable
 
     protected function getCacheControlHeader()
     {
-        $parts = array();
         ksort($this->cacheControl);
-        foreach ($this->cacheControl as $key => $value) {
-            if (true === $value) {
-                $parts[] = $key;
-            } else {
-                if (preg_match('#[^a-zA-Z0-9._-]#', $value)) {
-                    $value = '"'.$value.'"';
-                }
 
-                $parts[] = "$key=$value";
-            }
-        }
-
-        return implode(', ', $parts);
+        return HeaderUtils::toString($this->cacheControl, ',');
     }
 
     /**
@@ -320,12 +308,8 @@ class HeaderBag implements \IteratorAggregate, \Countable
      */
     protected function parseCacheControl($header)
     {
-        $cacheControl = array();
-        preg_match_all('#([a-zA-Z][a-zA-Z_-]*)\s*(?:=(?:"([^"]*)"|([^ \t",;]*)))?#', $header, $matches, PREG_SET_ORDER);
-        foreach ($matches as $match) {
-            $cacheControl[strtolower($match[1])] = isset($match[3]) ? $match[3] : (isset($match[2]) ? $match[2] : true);
-        }
+        $parts = HeaderUtils::split($header, ',=');
 
-        return $cacheControl;
+        return HeaderUtils::combine($parts);
     }
 }