alert() not working in codepen, consider alternative onclick functions for tutorial

https://github.com/reactjs/reactjs.org/blob/master/content/tutorial/tutorial.md

At some part of this tutorial (um, line 238 of that md file), I was asked to give the squares an onclick function of alert("click"). However, apparently Chrome has blocked this from running in codepen (A different origin subframe tried to create a JavaScript dialog. This is no longer allowed and was blocked. See https://www.chromestatus.com/feature/5148698084376576 for more details.), and can be confusing to people.

The next best alternative for alert that I can think of is console.log, and logged messages can be seen in both the browser's console and codepen's console.

Abre tutorial/tutorial.md cerca de la línea 238 y revisa el controlador alert("click") de los cuadrados en el ejemplo de CodePen. Verifica que una alternativa como console.log funcione tanto en la consola del navegador como en las consolas de CodePen; el trabajo estará terminado cuando el ejemplo ya no active el diálogo bloqueado y siga siendo comprensible.