for http://my.candycane.jp/issues/show/483
'extra' has been replaced 'mount_options'

https://github.com/mitchellh/vagrant/blob/master/CHANGELOG.md#130-september-5-2013
Merge pull request #225 from okonomi/fix/vagrantfile-update

Vagrantfile: updated shared folders option
Merge branch 'master' of git://github.com/yandod/candycane