docs: fix upgrade_415.rst

The explanation was not accurate.

Co-authored-by: Michal Sniatala <michal@sniatala.pl>

Author: kenjis

user_guide_src/source/installation/upgrade_415.rst

@@ -56,7 +56,7 @@ Protecting **GET** method needs only when you use ``form_open()`` auto-generatio
 CURLRequest header change
 -------------------------
 
-Because of a bug, the previous version of ``CURLRequest`` sends the request headers from the browser request.
+In the previous version, if you didn't provide your own headers, ``CURLRequest`` would send the request-headers from the browser.
 The bug was fixed. If your requests depend on the headers, your requests might fail after upgrading.
 In this case, add the necessary headers manually.
 See `CURLRequest Class <../libraries/curlrequest.html#headers>`_ for how to add.