Subject: [codesprints] Note the idnits upgrade

From: Robert Sparks <[email-masked]>
Date: Tue, 9 Oct 2018 17:11:05 -0500

If you _aren't_ using Docker, you'll need to update your working 
environment with a new version of idnits.

You'll need 2.16.0 for the tests to all pass correctly.

RjS