GitDownloader.php: better escaping for Windows

Compability for Windows usernames and passwords. When usernames and passwords contain characters that are rawurlencoded to a string containing a % sign (e.g. @ becomes %40), the procent was replaced with a space. Git can there not authenticate.
Update GitDownloader.php

PHP 5.3. compat.
Update GitDownloader.php
#3297 ProcessUtil class using ProcessUtil of Symfony Console
ProcessExecutor::escape
Merge remote-tracking branch 'frederikbosch/patch-1'
Fix formatting
Update deps