Fix to find dotnet root on 64-bits darwin system

[LeeDongGeon1996]

• Fix to find dotnet root on 64-bits darwin system
• Ref: https://docs.python.org/3/library/platform.html#cross-platform
• Fixes #36

[filmor]

Thank you, I'll release this later today!

[LeeDongGeon1996]

@filmor Thanks for your work🙂