update docs for discord api error (#1575)

* aaaaa

* Update DiscordAPIError.js

src/client/rest/DiscordAPIError.js

@@ -1,5 +1,6 @@
 /**
  * Represents an error from the Discord API.
+ * @extends Error
  */
 class DiscordAPIError extends Error {
   constructor(error) {
@@ -20,6 +21,7 @@ class DiscordAPIError extends Error {
    * @param {Object} obj Discord errors object
    * @param {string} [key] Used internally to determine key names of nested fields
    * @returns {string[]}
+   * @private
    */
   static flattenErrors(obj, key = '') {
     let messages = [];