Update jfryman/puppet-nginx dependency to include $index_files

This puphpet interface to configure properly projects which don't use
index.php as the entry point to the application. An example is Symfony2

Reference commit: https://github.com/jfryman/puppet-nginx/commit/04c541

**Note:** I couldn't set up the vagrant box for puphpet to run the tests, and as such i'm not sure if this breaks anything.