Merge pull request facebook-csharp-sdk#337 from nguyenquyhy/master

Fix facebook-csharp-sdk#336: FacebookClient throws NullReferenceException when calling GetTaskAsync in Windows 10 app

updated version to v7.0.9-beta

updated version to v7.0.7-beta

updated to 7.0.6 for production release

updated version to v7.0.5-beta

updated version to v7.0.3-alpha

updated version to v7.0.1-alpha

updated version to v7.0.0-alpha

updated version to v6.8.0

updated version to v6.7.0