Unable to build Universal 10 with .NET scripting backend, "SerializationBinder" missing from mscorlib.

Repro steps:
1. open project "HttpTest.zip".
2. build to WSA Universal 10 with .NET backend.
3. observe errors in the console for the following errors:
error CS7069: Reference to type 'SerializationBinder' claims it is defined in 'mscorlib', but it could not be found.

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By design:
WSA doesn't use Mono, it uses .NET for UWP.
Here's a list of available classes - https://msdn.microsoft.com/en-us/library/windows/apps/br230232.aspx
SerializationBinder is not available in .NET for UWP.