bug#33081: 27.0.50; Docstring of gnus-article-treat-fold-newsgroups is wrong

[Filipp Gunbin]

Docstring of gnus-article-treat-fold-newsgroups looks like it's
copy-pasted from gnus-article-treat-unfold-headers:

"Unfold folded message headers.
Only the headers that fit into the current window width will be
unfolded."

Thanks.

In GNU Emacs 27.0.50 (build 5, x86_64-apple-darwin17.7.0, NS appkit-1561.60 
Version 10.13.6 (Build 17G65))
 of 2018-10-18 built on fgunbin.playteam.ru
Repository revision: 46106eec16ddb2294e06f9e482b9183777b90014
System Description:  Mac OS X 10.13.6