Updated `omnibus` with `*.metadata.json` fixes

The latest version of Omnibus contains important fixes for the generated
metadata files. In particular the following items are fixed:

* `*.metadata.json` files are properly copied over to $PWD/pkg at build
completion on Windows builders: opscode/omnibus-ruby@f90842baf6
* Latest version of Ohai properly retrieves platform and platform
version on Windows builders: opscode/omnibus-ruby@bfedf87e6a
* Build iteration has been added to `*.metadata.json` for use in
publishing tasks: opscode/omnibus-ruby@3dfd9b3773
Updated `omnibus-software` for compat with latest `omnibus`
Merge pull request #194 from opscode/schisamo/updated-omnibus

Updated `omnibus` with `*.metadata.json` fixes