Update to drupal 8.0.0-rc1. For more information, see https://www.drupal.org/node/2582663

vendor/symfony/class-loader/Tests/Fixtures/psr-4/Class_With_Underscores.php

@@ -0,0 +1,7 @@
+<?php
+
+namespace Acme\DemoLib;
+
+class Class_With_Underscores
+{
+}

vendor/symfony/class-loader/Tests/Fixtures/psr-4/Foo.php

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+<?php
+
+namespace Acme\DemoLib;
+
+class Foo
+{
+}

vendor/symfony/class-loader/Tests/Fixtures/psr-4/Lets/Go/Deeper/Class_With_Underscores.php

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+<?php
+
+namespace Acme\DemoLib\Lets\Go\Deeper;
+
+class Class_With_Underscores
+{
+}

vendor/symfony/class-loader/Tests/Fixtures/psr-4/Lets/Go/Deeper/Foo.php

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+<?php
+
+namespace Acme\DemoLib\Lets\Go\Deeper;
+
+class Foo
+{
+}