bug#26182: cond-expand doc omits guile-2.2 feature

[Andy Wingo]

On Mon 20 Mar 2017 02:22, Zefram <zef...@fysh.org> writes:

> As implemented in Guile 2.2.0, the unlisted feature guile-2.2 is also
> recognised by cond-expand.

Added to doc; tx for report.

Andy