[osis-core] Manual: revisionDesc date format

[Chris Little]

The manual reads:

6.1. The Revision Description
To record changes or edits to the text, authors and editors are 
encouraged to insert a change element every time significant editing is 
done. Each change element should contain a date element which says when 
those edits were completed, in the form

     yyyy:mm:ddThh:mm:ss



Should this read "yyyy-mm-ddThh:mm:ss" instead?  I've never seen this 
format before and don't find it in any of my searching.

--Chris