Drupal 8.0.0 beta 12. More info: https://www.drupal.org/node/2514176

core/vendor/symfony/browser-kit/CHANGELOG.md

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+CHANGELOG
+=========
+
+2.3.0
+-----
+
+ * [BC BREAK] `Client::followRedirect()` won't redirect responses with
+   a non-3xx Status Code and `Location` header anymore, as per 
+   http://tools.ietf.org/html/rfc2616#section-14.30
+
+ * added `Client::getInternalRequest()` and `Client::getInternalResponse()` to
+   have access to the BrowserKit internal request and response objects
+
+2.1.0
+-----
+
+ * [BC BREAK] The CookieJar internals have changed to allow cookies with the
+   same name on different sub-domains/sub-paths