Get or change the update channel.

== USAGE
  omf channel         Print the currently selected update channel
  omf channel <name>  Switch to the given update channel

== DESCRIPTION
Two channels are available by default: the _stable_ channel provides stable
updates with the latest tagged version of Oh My Fish, and _dev_ which provides
the latest changes under development. The update channel currently set
determines what version *omf update* will upgrade to.

== EXAMPLES
  omf channel
  omf channel stable
  omf channel dev
