Docs: InternalsVisibleTo attribute docs incorrect

[dtchepak]

As per this SO comment, the How NSub Works docs are incorrect.

Use [assembly: InternalsVisibleTo(InternalsVisible.ToDynamicProxyGenAssembly2)] in the test assembly so that the internal member can be overridden.

should be:

Use [assembly: InternalsVisibleTo(InternalsVisible.ToDynamicProxyGenAssembly2)] in the assembly under test so that the internal member can be overridden.