Fixes variable export for Windows.
Issue: https://github.com/laravel/laravel/issues/1870
Fix in commit https://github.com/laravel/laravel/commit/678b92ef85ce0258eb9a6ac57bb26fca9480e430 does not work.

Signed-off-by: aeberhardo <aeberhard@gmx.ch>
Merge pull request #1994 from aeberhardo/bug/putenv

Fixes variable export for Windows.