switch to cdn endpoints, add guild splash url (#932)

src/structures/Guild.js

@@ -241,6 +241,16 @@ class Guild {
     return Constants.Endpoints.guildIcon(this.id, this.icon);
   }
 
+  /**
+   * Gets the URL to this guild's splash (if it has one, otherwise it returns null)
+   * @type {?string}
+   * @readonly
+   */
+  get splashURL() {
+    if (!this.splash) return null;
+    return Constants.Endpoints.guildSplash(this.id, this.splash);
+  }
+
   /**
    * The owner of the guild
    * @type {GuildMember}