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

vendor/composer/installers/src/Composer/Installers/SilverStripeInstaller.php

@@ -0,0 +1,36 @@
+<?php
+namespace Composer\Installers;
+
+use Composer\Package\PackageInterface;
+
+class SilverStripeInstaller extends BaseInstaller
+{
+    protected $locations = array(
+        'module' => '{$name}/',
+        'theme'  => 'themes/{$name}/',
+    );
+
+    /**
+     * Return the install path based on package type.
+     *
+     * Relies on built-in BaseInstaller behaviour with one exception: silverstripe/framework
+     * must be installed to 'sapphire' and not 'framework' if the version is <3.0.0
+     *
+     * @param  PackageInterface $package
+     * @param  string           $frameworkType
+     * @return string
+     */
+    public function getInstallPath(PackageInterface $package, $frameworkType = '')
+    {
+        if (
+            $package->getName() == 'silverstripe/framework'
+            && preg_match('/^\d+\.\d+\.\d+/', $package->getVersion())
+            && version_compare($package->getVersion(), '2.999.999') < 0
+        ) {
+            return $this->templatePath($this->locations['module'], array('name' => 'sapphire'));
+        } else {
+            return parent::getInstallPath($package, $frameworkType);
+        }
+
+    }
+}