enhancement(Activity): add toString method (#2313)

src/structures/Presence.js

@@ -134,6 +134,14 @@ class Activity {
     );
   }
 
+  /**
+   * When concatenated with a string, this automatically returns the activities's name instead of the Activity object.
+   * @returns {string}
+   */
+  toString() {
+    return this.name;
+  }
+
   _clone() {
     return Object.assign(Object.create(this), this);
   }