update gosdk/io to v6
change  conf.UP_HOST to http://up.qiniu.com
recover rpc.logger support
fix api.io
fix ploicy.Expires buf
wMerge remote-tracking branch 'qiniu/develop' into feature/update_io_to_v6
update
Merge pull request #67 from wangtuanjie/feature/update_io_to_v6

update gosdk/io to v6