fix: re-add highest property to RoleStore and GuildMemberRoleStore

closes #2302

src/stores/GuildMemberRoleStore.js

@@ -106,7 +106,7 @@ class GuildMemberRoleStore extends DataStore {
    * @readonly
    */
   get highest() {
-    return this.reduce((prev, role) => !prev || role.comparePositionTo(prev) > 0 ? role : prev);
+    return this.reduce((prev, role) => role.comparePositionTo(prev) > 0 ? role : prev, this.first());
   }
 
   /**

src/stores/RoleStore.js

@@ -55,6 +55,15 @@ class RoleStore extends DataStore {
     });
   }
 
+  /**
+   * The role with the highest position in the store
+   * @type {Role}
+   * @readonly
+   */
+  get highest() {
+    return this.reduce((prev, role) => role.comparePositionTo(prev) > 0 ? role : prev, this.first());
+  }
+
   /**
    * Data that can be resolved to a Role object. This can be:
    * * A Role