Fixed typo at docs/examples/rtl/index.php

The filename generated at dist/css/ called 'bootstrap-rtl.min.css'.
Merge pull request #13018 from ORiON-/master

Fixed typo at docs/examples/rtl/index.php
Run usebanner before cssmin.
Simplify tasks a little bit.
Merge pull request #13012 from twbs/banner