Add Symfony4 support.

Author: makasim

Symfony/NullTransportFactory.php

@@ -66,7 +66,9 @@ public function createContext(ContainerBuilder $container, array $config)
         $factoryId = sprintf('enqueue.transport.%s.connection_factory', $this->getName());
 
         $contextId = sprintf('enqueue.transport.%s.context', $this->getName());
+
         $context = new Definition(NullContext::class);
+        $context->setPublic(true);
         $context->setFactory([new Reference($factoryId), 'createContext']);
 
         $container->setDefinition($contextId, $context);
@@ -80,6 +82,7 @@ public function createContext(ContainerBuilder $container, array $config)
     public function createDriver(ContainerBuilder $container, array $config)
     {
         $driver = new Definition(NullDriver::class);
+        $driver->setPublic(true);
         $driver->setArguments([
             new Reference(sprintf('enqueue.transport.%s.context', $this->getName())),
             new Reference('enqueue.client.config'),

composer.json

@@ -14,8 +14,8 @@
         "enqueue/enqueue": "^0.8@dev",
         "enqueue/test": "^0.8@dev",
         "queue-interop/queue-spec": "^0.5.3@dev",
-        "symfony/dependency-injection": "^2.8|^3",
-        "symfony/config": "^2.8|^3"
+        "symfony/dependency-injection": "^2.8|^3|^4",
+        "symfony/config": "^2.8|^3|^4"
     },
     "autoload": {
         "psr-4": { "Enqueue\\Null\\": "" },