Improve Duration#toHuman docblock (#1534)

src/duration.js

@@ -484,9 +484,10 @@ export default class Duration {
 
   /**
    * Returns a string representation of a Duration with all units included.
-   * To modify its behavior use the `listStyle` and any Intl.NumberFormat option, though `unitDisplay` is especially relevant.
-   * @see https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl/NumberFormat
-   * @param opts - On option object to override the formatting. Accepts the same keys as the options parameter of the native `Int.NumberFormat` constructor, as well as `listStyle`.
+   * To modify its behavior, use `listStyle` and any Intl.NumberFormat option, though `unitDisplay` is especially relevant.
+   * @see https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl/NumberFormat/NumberFormat#options
+   * @param {Object} opts - Formatting options. Accepts the same keys as the options parameter of the native `Intl.NumberFormat` constructor, as well as `listStyle`.
+   * @param {string} [opts.listStyle='narrow'] - How to format the merged list. Corresponds to the `style` property of the options parameter of the native `Intl.ListFormat` constructor.
    * @example
    * ```js
    * var dur = Duration.fromObject({ days: 1, hours: 5, minutes: 6 })