docs/typings(MessageAttachment): mark spoiler as readonly, order spoiler in typings (#3714)

src/structures/MessageAttachment.js

@@ -84,6 +84,7 @@ class MessageAttachment {
   /**
    * Whether or not this attachment has been marked as a spoiler
    * @type {boolean}
+   * @readonly
    */
   get spoiler() {
     return Util.basename(this.url).startsWith('SPOILER_');

typings/index.d.ts

@@ -1027,9 +1027,9 @@ declare module 'discord.js' {
 		public name?: string;
 		public proxyURL: string;
 		public size: number;
+		public readonly spoiler: boolean;
 		public url: string;
 		public width: number | null;
-		public readonly spoiler: boolean;
 		public setFile(attachment: BufferResolvable | Stream, name?: string): this;
 		public setName(name: string): this;
 		public toJSON(): object;