Fix example to use Video instead of DeliveryUsage

This fixes the import example to ensure the Video class is being imported instead of DeliveryUsage. Matches the convention of all other classes.

Author: davekiss

src/video/resources/deliveryUsage.js

@@ -13,7 +13,7 @@ const PATH = '/video/v1/delivery-usage';
  * DeliveryUsage Class - Provides access to the Mux Video Delivery Usage API
  *
  * @example
- * const { DeliveryUsage } = new Mux(accessToken, secret);
+ * const { Video } = new Mux(accessToken, secret);
  *
  * // List delivery usage within a timeframe
  * Video.DeliveryUsage.list({timeframe: [1574076240, 1573471440]});
@@ -25,7 +25,7 @@ class DeliveryUsage extends Base {
    * @returns {Promise} - Returns a resolved Promise with a response from the Mux API
    *
    * @example
-   * const { DeliveryUsage } = new Mux(accessToken, secret);
+   * const { Video } = new Mux(accessToken, secret);
    *
    * // List all delivery usage for a Mux Environment within a timeframe
    * Video.DeliveryUsage.list({timeframe: [1574076240, 1573471440]});