Merge branch '2.8' into 3.2

* 2.8:
  Fixes #22264 - add support for Chrome headless, see also Seldaek/monolog#966
  bumped Symfony version to 2.8.20
  updated VERSION for 2.8.19
  updated CHANGELOG for 2.8.19
  Dont call sprintf() when no placeholders are used

Author: fabpot

Command/ContainerDebugCommand.php

@@ -173,11 +173,11 @@ protected function getContainerBuilder()
         }
 
         if (!$this->getApplication()->getKernel()->isDebug()) {
-            throw new \LogicException(sprintf('Debug information about the container is only available in debug mode.'));
+            throw new \LogicException('Debug information about the container is only available in debug mode.');
         }
 
         if (!is_file($cachedFile = $this->getContainer()->getParameter('debug.container.dump'))) {
-            throw new \LogicException(sprintf('Debug information about the container could not be found. Please clear the cache and try again.'));
+            throw new \LogicException('Debug information about the container could not be found. Please clear the cache and try again.');
         }
 
         $container = new ContainerBuilder();