slingshot: update.

* slingshot: Update.
* bootstrap.slingshot: Install latest revision.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>
specl: update to Specl 8 changes in hell.spawn.

* specs/posix_spec.yaml: Specl 8 no longer copies table entries
from require results into environments automatically, so make sure
we capture the table, and then use qualified access to spawn.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>
typo: the documentation directory is called doc, not docs!

* local.mk (dist_doc_DATA, MAINTAINERCLEANFILES): Use correctly
spelled 'doc' instead of previous typo, 'docs'.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>