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>

laravel/cli/tasks/test/runner.php

@@ -89,7 +89,7 @@ class Runner extends Task {
 		$esc_path = escapeshellarg($path);
 
 		putenv('LARAVEL_ENV='.Request::env());
-		passthru('LARAVEL_ENV='.Request::env().' phpunit --configuration '.$esc_path, $status);
+		passthru('phpunit --configuration '.$esc_path, $status);
 
 		@unlink($path);