Update AutoloadGenerator.php

This should fix an issue with this commit:
https://github.com/composer/composer/commit/87a42c2f01936e6fd8973fac159dc8117114bebc

This commit is causing a parse error in autoload_namespaces.php:
return array(
    'zsql' => 'phar://' . '$vendorDir . '/jbboehr/zsql/build/zsql.phar',

A similar problem happens when using autoload.files as well.
Merge pull request #1856 from jbboehr/patch-1

Update AutoloadGenerator.php
Retry file downloads 3 times before giving up in case of basic network failure