only write file caches if minutes is greater than zero.

laravel/cache/drivers/file.php

@@ -67,6 +67,8 @@ class File extends Driver {
 	 */
 	public function put($key, $value, $minutes)
 	{
+		if ($minutes <= 0) return;
+
 		$value = $this->expiration($minutes).serialize($value);
 
 		file_put_contents($this->path.$key, $value, LOCK_EX);