doc: correct argument order for error matcher.
doc: correct argument order for error matcher.

The order of error matcher arguments was reversed with Specl 5.
* doc/specl.md (Pending Examples): Fix error matcher argument
order to match contemporary usage.

Signed-off-by: Gary V. Vaughan <f9023000f29773649f3850298becb9544b5fd6a9@gnu.org>

gvvaughan/specl