Oxyplot.Core nuget packages still refers to PCL target framework in NET40 folder.

Oxyplot.Core nuget packages contains an Oxyplot.dll PCL assembly in the NET40 folder. 
Firstly ,this was due to a wrong referencing in the projects of the OxyPlot.AppVeyor.sln
Secondly, OxyPlot.GtkSharp is referencing Oxyplot (PCL) while this project is targeted to NET4 framework and it overwrites the NET4 assembly version.

See issue #254 for further information.