Add ref assemblies

Author: akoeplinger

.nuget/packages.config

@@ -1,7 +1,8 @@
 <?xml version="1.0" encoding="utf-8"?>
 <packages>
+  <package id="Microsoft.NETFramework.ReferenceAssemblies" version="1.0.3" developmentDependency="true" />
   <package id="Microsoft.Web.SkipStrongNames" version="1.0.0" />
   <package id="Microsoft.Web.StyleCop" version="1.0.0" />
   <package id="StyleCop" version="5.0.0" />
   <package id="xunit.runner.msbuild" version="2.4.2" targetFramework="net452" />
-</packages>
+</packages>