Add ref to .core.nuspec

Author: mythz

src/ServiceStack.Admin.sln

@@ -1,14 +1,15 @@
 
 Microsoft Visual Studio Solution File, Format Version 12.00
 # Visual Studio 15
-VisualStudioVersion = 15.0.27130.2003
+VisualStudioVersion = 15.0.27130.2010
 MinimumVisualStudioVersion = 10.0.40219.1
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "ServiceStack.Admin", "ServiceStack.Admin\ServiceStack.Admin.csproj", "{C6EB693E-64D1-4271-BE68-0B78D186003E}"
 EndProject
 Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "build", "build", "{2A9F798E-B4A8-4089-AF2D-E841BB354244}"
 	ProjectSection(SolutionItems) = preProject
 		..\build\build.bat = ..\build\build.bat
 		..\build\build.proj = ..\build\build.proj
+		..\NuGet\ServiceStack.Admin.Core\servicestack.admin.core.nuspec = ..\NuGet\ServiceStack.Admin.Core\servicestack.admin.core.nuspec
 		..\NuGet\ServiceStack.Admin\servicestack.admin.nuspec = ..\NuGet\ServiceStack.Admin\servicestack.admin.nuspec
 	EndProjectSection
 EndProject