Update free-programming-books.md

Fixed typo.
[es] sorting some other titles
[es] Added Aprenda a programar como si estuviera en primero
Merge pull request #744 from esparta/master

[es] New agnostic book and more ordering titles
fix #714, The Art of Assembly Language Programming

Access to previous link was forbidden. The new link now should works.
Merge pull request #745 from matematikaadit/patch-2

fix #714, The Art of Assembly Language Programming
Retirando link do Padrões JS

Licença gera dupla interpretação, sendo assim, após tradução do JavaScript Eloquente irei contatar o autor para obter uma permissão/ou não, para tal.
Merge pull request #746 from ericdouglas/patch-1

Retirando link do Padrões JS
[es] Added two C# books
Merge pull request #747 from esparta/master

[es] Added two C# books
[es] Added Fundamentos de Sistemas Operativos
Merge pull request #748 from esparta/master

[es] Added Operating System Book
Added a new PostgreSQL book
Added PostgreSQL to the index
Merge pull request #750 from therufa/master

Added new PostgreSQL book
[fa_IR] Ubuntu -> Persian Ubuntu Book
Merge pull request #751 from 0x55D/persian-ubuntubook

[fa_IR] Ubuntu -> Persian Ubuntu Book
[es] Removing duplicated Pro-git book
[es] Adding Programación concurrente y en tiempo real
Merge pull request #752 from esparta/master

[es] Removing duplicates & added book about concurrent programming