convert encoding of file path from utf8-mac to utf-8

MacOS uses not UTF8 but UTF8-MAC for file path name encoding.
Some japanese characters have different byte sequence between UTF8 and UTF8-MAC.
This causes url encoded path in UTF8-MAC cannot be accessible when we put Japanese URL in browser.
So I made a change to convert path name from UTF8-MAC to UTF8 before upload to S3 to avoid this kind of problems.