Update sitemap

## Description

Update `SITE_URL` inside [constants.ts](https://github.com/hozlucas28/Mercado-Play/blob/Master/src/constants.ts) and [robots.txt](https://github.com/hozlucas28/Mercado-Play/blob/Master/public/robots.txt).

## Expected behavior

Correct generation of a sitemap based on `SITE_URL`.