OxyPlot.WindowsForms_NET40.csproj still refers to Oxyplot PCL project. #250
 - Update the csproj to refers to OxyPlot.WindowsForms_NET40.csproj
Merge pull request #251 from thomsonreuters/NET40.Compatibility

OxyPlot.WindowsForms_NET40.csproj still refers to Oxyplot PCL project