Don’t run BFF colon/comma unit tests on Windows
Don’t run BFF colon/comma unit tests on Windows

This will stop the following failures when Appveyor executes the unit
tests:

```
Failure/Error: FileUtils.touch(path)
 
Errno::EINVAL:
  Invalid argument - /projects/omnibus/spec/tmp/staging/dir/man3/App::Cpan.3
# ./spec/support/file_helpers.rb:36:in `create_file'
# ./spec/unit/packagers/bff_spec.rb:147:in `block (4 levels) in <module:Omnibus>'
 
```
jamesn/omnibus,Altiscale/omnibus,rapid7/omnibus,rapid7/omnibus,higanworks/omnibus,rapid7/omnibus,szechyjs/omnibus,jamesn/omnibus,higanworks/omnibus,jamesn/omnibus,chef/omnibus,DataDog/omnibus-ruby,szechyjs/omnibus,Scalr/omnibus,strangelittlemonkey/omnibus,Altiscale/omnibus,strangelittlemonkey/omnibus,DataDog/omnibus-ruby,chef/omnibus,Altiscale/omnibus,Scalr/omnibus,higanworks/omnibus,DataDog/omnibus-ruby,szechyjs/omnibus,strangelittlemonkey/omnibus,chef/omnibus,Scalr/omnibus