REVIEW ONLY - dirvish: bump submodule

This is needed to create 'latest' symlinks in the backup vaults, which can be targeted for offsite backup of the latest data. @domcleal @skottler if you wish to review the actual changes they're here:

https://github.com/GregSutcliffe/puppet-dirvish/commit/d781ec065b38d932bd13087035f79c3b0e8adcd2
https://github.com/GregSutcliffe/puppet-dirvish/commit/0e1e2e14ba0b6070b6d6885ec708b4c8e144ff77
https://github.com/GregSutcliffe/puppet-dirvish/commit/a745461f6602e204b40ce09ff6627b6a6b7597a2

I've tested it here at home, so review or not, I'll merge it tomorrow :p