Update to Drupal 8.1.0. For more information, see https://www.drupal.org/drupal-8.1.0-release-notes

vendor/symfony/http-foundation/composer.json

@@ -16,19 +16,24 @@
         }
     ],
     "require": {
-        "php": ">=5.3.9"
+        "php": ">=5.3.9",
+        "symfony/polyfill-php54": "~1.0",
+        "symfony/polyfill-php55": "~1.0",
+        "symfony/polyfill-mbstring": "~1.1"
     },
     "require-dev": {
-        "symfony/expression-language": "~2.4"
+        "symfony/expression-language": "~2.4|~3.0.0"
     },
     "autoload": {
         "psr-4": { "Symfony\\Component\\HttpFoundation\\": "" },
-        "classmap": [ "Resources/stubs" ]
+        "exclude-from-classmap": [
+            "/Tests/"
+        ]
     },
     "minimum-stability": "dev",
     "extra": {
         "branch-alias": {
-            "dev-master": "2.7-dev"
+            "dev-master": "2.8-dev"
         }
     }
 }