bug#30297: 27.0.50; *Help* shows inaccurate arglist for json-parse-string

[Eli Zaretskii]

> From: "Basil L. Contovounesios" <contovob@tcd.ie>
> Date: Tue, 30 Jan 2018 23:31:29 +0000
> 
> Seen on latest master:
> 
> 1. emacs -Q
> 2. C-h f json-parse-string RET
> 
> *Help* reports the following arglist:
> 
>   (json-parse-string &key (OBJECT-TYPE 'hash-table))
> 
> despite mention of the positional argument STRING in the rest of the
> docstring.
> 
> Attached is a doc fix suggestion.

Philipp, any comments?

Thanks.