text: var expand = require("reducers/expand")
  var take = require("reducers/take")
  var callback = require("callback-reduce")
  
  module.exports = update
  
  function update(collection, selector, doc, options) {
      return take(expand(collection, function (collection) {
          return callback.call(collection, collection.update
              , selector, doc, options || {})
      }), 1)
  }
  