Merge branch '2.0.x' into 1.0.x

# Conflicts:
#	src/Resources/DependencyInjection/ExtractorChainCompilerPass.php

Author: allflame

src/Resources/DependencyInjection/ExtractorChainCompilerPass.php

@@ -18,11 +18,6 @@ public function process(ContainerBuilder $container)
         $definition = $container->getDefinition('jaeger.context.extractor.chain');
         foreach ($container->findTaggedServiceIds('jaeger.context.extractor') as $id => $tags) {
             foreach ($tags as $tag) {
-                if (false === array_key_exists('alias', $tag)) {
-                    throw new \RuntimeException(
-                        sprintf('Required tag field %s is missing from definition', 'alias')
-                    );
-                }
                 $priority = array_key_exists('priority', $tag) ? $tag['priority'] : 0;
                 $definition->addMethodCall('add', [new Reference($id), $priority]);
             }