fix issue symfony#8171 on configuration tree for twig extension -- pairing up with @cordoval

Author: mdavis1982

src/Symfony/Bundle/TwigBundle/DependencyInjection/Configuration.php

@@ -136,6 +136,7 @@ private function addTwigOptions(ArrayNodeDefinition $rootNode)
                 ->scalarNode('optimizations')->end()
                 ->arrayNode('paths')
                     ->normalizeKeys(false)
+                    ->useAttributeAsKey('paths')
                     ->beforeNormalization()
                         ->always()
                         ->then(function ($paths) {