code: def update(self, collection_id, title=None, description=None, private=False):
          
          url = "/collections/%s" % collection_id
          data = {
              "title": title,
              "description": description,
              "private": private
          }
          result = self._put(url, data=data)
          return CollectionModel.parse(result)
docs: Update an existing collection belonging to the logged-in user.
          This requires the 'write_collections' scope.
  
          :param collection_id [string]: The collection’s ID. Required.
          :param title [string]: The title of the collection. (Required.)
          :param description [string]: The collection’s description. (Optional.)
          :param private [boolean]: Whether to make this collection private. (Optional; default false).
          :return: [Collection]: The Unsplash Collection.