Managed Union script (user's script) throws an exception when using .NET 4.6.
With .NET 3.5 everything works as expected.

Steps to reproduce:
1. Open attached project (Managed Union.zip)
2. Set Scripting Runtime version to .NET 4.6
3. Enter Play mode

Result: Exception is thrown while trying to create a new instance of EnumUnion:
TypeLoadException: Could not find method due to a type load error

Reproduced with: 2017.3.0a3, 2017.2.0b6, 2017.1.0p2.
Not reproduced with: 5.6 (no .NET 4.6 feature)