backport: Message#url getter

src/structures/Message.js

@@ -215,6 +215,15 @@ class Message {
     return this.channel.guild || null;
   }
 
+  /**
+   * The url to jump to the message
+   * @type {string}
+   * @readonly
+   */
+  get url() {
+    return `https://discordapp.com/channels/${this.guild ? this.guild.id : '@me'}/${this.channel.id}/${this.id}`;
+  }
+
   /**
    * The message contents with all mentions replaced by the equivalent text.
    * If mentions cannot be resolved to a name, the relevant mention in the message content will not be converted.