Fixed nuspec definition to be inline with Nuget spesifcation for TargetFrameworks. fixes beto-rodriguez/Live-Charts#221
Fixed nuspec definition to be inline with Nuget spesifcation for TargetFrameworks. fixes beto-rodriguez/Live-Charts#221

DeadlyEmbrace/Live-Charts,rusanov-vladimir/Live-Charts,beto-rodriguez/Live-Charts,hulihutu9/Live-Charts,henninltn/Live-Charts