Support for /update specific channels

[jsloyer]

The rest of nuts supports channels however the /update route does not.

Currently the routes are the following.

/update/:platform/:version
/update/:platform/:version/RELEASES

I am proposing the following, adding an optional channel.

/update/:platform/:version/:channel
/update/:platform/:version/RELEASES/:channel

I can submit a PR for this but I want buy in before submitting. @SamyPesse thoughts?

[razvanilin]

+1 I came across this now too. I was versioning my releases with channels but the auto-update doesn't work properly if I go down that way.

[fredericlefeurmou]

Is this going to be implemented?

[rahilsondhi]

Isn't this a dupe of https://github.com/GitbookIO/nuts/pull/95, which is done?