code: function changeMetaState(uri, update) {
    return getMeta(uri)
      .then(old => mergeNewAndOldMeta(old, update))
      .then(updatedMeta => putMeta(uri, updatedMeta));
  }
docs: Given a uri and an object that is an
  update, retreive the old meta, merge
  the new and old and then put the merge
  to the db.
  
  @param {String} uri
  @param {Object} update
  @returns {Promise}