CFC: nameMap property of Link type

This is a call for consensus on a new erratum for the Activity 
Vocabulary document. The motivating issue is found here:

https://github.com/w3c/activitystreams/issues/486

To summarize, the properties of the `Link` type are enumerated in the 
Activity Vocabulary document, but do not include the `nameMap` property, 
which is a valid variation on `name` for multilingual support. We have 
typically included the `*Map` properties by implication, which has been 
a source of confusion for developers, so this is a step in the direction 
of more clarity.

Based on the report, we delved into which other properties of `Link` 
aren't enumerated, and came up with others. The proposed erratum is:

/- Section 4.2 lists the possible properties of a `Link` object. This 
list omits `nameMap`, `preview`, `attributedTo`. The full list should 
be: id | name | nameMap | hreflang | mediaType | rel | height | width | 
preview | attributedTo./


https://github.com/w3c/activitystreams/pull/553

This CFC is asking for feedback from the SocialCG on this change. If 
there are no outstanding objections in 14 days for this question, I will 
merge this erratum and apply the change to the editor's draft of 
Activity Vocabulary.

Evan