typo: update error link in App.ts (#2260)

Author: ChinoUkaegbu

src/App.ts

@@ -1303,7 +1303,7 @@ export default class App<AppCustomContext extends StringIndexed = StringIndexed>
 
     if (authorize === undefined && !usingOauth) {
       throw new AppInitializationError(
-        `${tokenUsage} \n\nSince you have not provided a token or authorize, you might be missing one or more required oauth installer options. See https://slack.dev/bolt-js/concepts#authenticating-oauth for these required fields.\n`,
+        `${tokenUsage} \n\nSince you have not provided a token or authorize, you might be missing one or more required oauth installer options. See https://slack.dev/bolt-js/concepts/authenticating-oauth for these required fields.\n`,
       );
     } else if (authorize !== undefined && usingOauth) {
       throw new AppInitializationError(`You cannot provide both authorize and oauth installer options. ${tokenUsage}`);