window设置prefix时路径错误

[ScorpiusJin]

$prefix = 'flysystem-oss/ddd/aaa/';

$flysystem->write('file2.md', 'contents');

在windows下执行，上传到oss的文件路径为
 "oss://flysystem-oss/ddd/aaa\file2.md"

flysystem-oss/src/OssAdapter.php

Line 126 in 730a3c6

$this->prefixer = new PathPrefixer($prefix, DIRECTORY_SEPARATOR);

$this->prefixer = new PathPrefixer($prefix, '/');

修改后windows上传oss路径正常