feat(DiscordAPIError): add method property (#2530)

src/rest/DiscordAPIError.js

@@ -3,12 +3,18 @@
  * @extends Error
  */
 class DiscordAPIError extends Error {
-  constructor(path, error) {
+  constructor(path, error, method) {
     super();
     const flattened = this.constructor.flattenErrors(error.errors || error).join('\n');
     this.name = 'DiscordAPIError';
     this.message = error.message && flattened ? `${error.message}\n${flattened}` : error.message || flattened;
 
+    /**
+     * The HTTP method used for the request
+     * @type {string}
+     */
+    this.method = method;
+
     /**
      * The path of the request relative to the HTTP endpoint
      * @type {string}

src/rest/handlers/RequestHandler.js

@@ -80,7 +80,8 @@ class RequestHandler {
             this.queue.unshift(item);
             finish(1e3 + this.client.options.restTimeOffset);
           } else {
-            item.reject(err.status >= 400 && err.status < 500 ? new DiscordAPIError(res.request.path, res.body) : err);
+            item.reject(err.status >= 400 && err.status < 500 ?
+              new DiscordAPIError(res.request.path, res.body, res.request.method) : err);
             finish();
           }
         } else {