Update SOTD in preparation for CR

[nigelmegitt]

As per https://lists.w3.org/Archives/Member/chairs/2018JanMar/0034.html, update the spec to point to Process 2018.

[palemieux]

The SotD always point to the latest published process. See spec/status.xml.

[nigelmegitt]

Hmm, looking at https://www.w3.org/TR/ttml2/ the SOTD has two references to the Process:

In the third paragraph:

... following the procedures set out for the W3C Process ...

Where Process is a link to https://www.w3.org/Consortium/Process/ which is the current operative version.

Then the last paragraph is:

This document is governed by the 1 March 2017 W3C Process Document.

Where there's a link to the 2017 dated version. I'm not sure how those two are generated, but they both need to point to the 2018 process (or the current operative one).