[Svn] [roundcube/roundcubemail] 3907fc: Fix compatibility to GuzzleHttp 6.5.x (#7634)

[Thomas B.]

  Branch: refs/heads/master
  Home:   https://github.com/roundcube/roundcubemail
  Commit: 3907fc161518fe5e6c177517632c1eaf5739d5ee
      https://github.com/roundcube/roundcubemail/commit/3907fc161518fe5e6c177517632c1eaf5739d5ee
  Author: Thomas Bruederli <thomas at roundcube.net>
  Date:   2020-09-28 (Mon, 28 Sep 2020)

  Changed paths:
    M program/include/rcmail_oauth.php

  Log Message:
  -----------
  Fix compatibility to GuzzleHttp 6.5.x (#7634)