function updateInvite(invite, collaboration, done) {
  var found = _.find(invite.collaborations, function(c) {
    return c.project === collaboration.project
  })
  // There is already an outstanding invite to this user, just push these additional perms onto the collaborations
  // list and send another email. We only push if they have not already been added to the invite.
  if (!found) {
    invite.update({$push:{collaborations: collaboration}}, function(err) {
      if (err) return done(err)
      // Invite updated, should probably send another email to recipient.
      return done(null, false, false)
    });
  } else {
    return done(null, false, true)
  }
}