crash under Xcode 8 beta 6 and Sierra PB 5

Am receiving this error after my project was built under Xcode 8 beta 6.
Looks like this new version of Xcode has introduced some new attributes...
The project is being generated by CMake -GXcode. Not sure if that makes any difference.

```
`/Users/me/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/xcodeproj-1.2.0/lib/xcodeproj/project/object.rb:321:in `configure_with_plist': [!] Xcodeproj doesn't know about the following attributes {"buildSettings"=>{}, "buildStyles"=>["334FFEFC836C4657AB4364F6", "06940D20BBA64B85AADC5514", "B19BE37AAEED49E5AAC3B7BC", "E12C544D5FF5410E9B3D0057"]} for the 'PBXProject' isa. (RuntimeError)
If this attribute was generated by Xcode please file an issue: https://github.com/CocoaPods/Xcodeproj/issues/new
from /Users/me/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/xcodeproj-1.2.0/lib/xcodeproj/project.rb:258:in `new_from_plist'
from /Users/me/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/xcodeproj-1.2.0/lib/xcodeproj/project.rb:202:in `initialize_from_file'
from /Users/me/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/xcodeproj-1.2.0/lib/xcodeproj/project.rb:102:in `open'
from krita_fix_targets.rb:49:in `'`
```

My ruby program runs when opening an older version (Xcode 8 beta 5 based) of my project (also generated by CMake 3.6)

Any help is greatly appreciated. Can help debug this on my side if necessary.

Regards, Patrice