Installed rubies (inside of node[:rbenv][:root]/versions) end up moded 0755

Despite the essential chmod on versions at the end of the default recipe, the subdirectory containing the actual installed version is not accessible to members of node[:rbenv][:group] other than node[:rbenv][:user]

I tried making
```ruby
    out = rbenv_command("install #{new_resource.name}")
```
in providers/ruby.rb into 
```ruby
    out = rbenv_command("install #{new_resource.name}", :umask =>'002')
```

to no avail. (I verified the umask was making it all the way to Mixlib::ShellOut::Unix#run_command, but the generated dir was still 755. So maybe call that a bug in sstephenson/ruby-build or the ruby Makefiles or something )

Adding a `recursive true` to the resource in the end of the default recipe also proved ineffective -- digging, this makes sense as all the ACL handling for directory resources is imported whole-cloth from files with no concept of recursion. :-(

Sooooo ... seems like the only option for the present, without requiring upstream changes to either chef or ruby-build is to add an explicit chmod on the directory after the install.