pt-br：translation of the index page in download section (#2208)
pt-br：translation of the index page in download section (#2208)

Translation of 'locale/pt-br/download/index.md' from en to pt-BR.
phillipj/new.nodejs.org,nodejs/new.nodejs.org,yous/new.nodejs.org,nodejs/new.nodejs.org,phillipj/new.nodejs.org,yous/new.nodejs.org