Update Curl to respect case-insensitive headers

According to RFC 2616 header names are case-insensitive: "Each header field consists of a name followed by a colon (":") and the field value. Field names are case-insensitive." - see https://tools.ietf.org/html/rfc2616#section-4.2

The "Set-Cookie" comparison in the previous version is case-sensitive and can cause problems with some (rare) HTTP servers.

Author: pmzandbergen

lib/internal/Magento/Framework/HTTP/Client/Curl.php

@@ -453,11 +453,11 @@ protected function parseHeaders($ch, $data)
             }
 
             if (strlen($name)) {
-                if ("Set-Cookie" == $name) {
-                    if (!isset($this->_responseHeaders[$name])) {
-                        $this->_responseHeaders[$name] = [];
+                if ("set-cookie" == strtolower($name)) {
+                    if (!isset($this->_responseHeaders['Set-Cookie'])) {
+                        $this->_responseHeaders['Set-Cookie'] = [];
                     }
-                    $this->_responseHeaders[$name][] = $value;
+                    $this->_responseHeaders['Set-Cookie'][] = $value;
                 } else {
                     $this->_responseHeaders[$name] = $value;
                 }