Add net461 target to work around ValueTuple missing method exceptions (#34)
Add net461 target to work around ValueTuple missing method exceptions (#34)

* Add net461 target to work around ValueTuple missing method exceptions

See dotnet/standard#567 for context here.
I ran into this while using `SetComparison.Compare(...)` which is all public DeepEquals API. This manifests itself like so:
```c#
	[{System.MissingMethodException}: 'Method not found: 'System.ValueTuple`2<DeepEqual.ComparisonResult,DeepEqual.IComparisonContext> DeepEqual.SetComparison.Compare(DeepEqual.IComparisonContext, System.Object, System.Object)'.']
```

jamesfoster/DeepEqual