Use sources.props

Directory.Build.props

@@ -5,6 +5,7 @@
 
   <Import Project="version.props" />
   <Import Project="build\dependencies.props" />
+  <Import Project="build\sources.props" />
 
   <PropertyGroup>
     <Product>Microsoft ASP.NET Core</Product>

NuGet.config

@@ -2,8 +2,5 @@
 <configuration>
   <packageSources>
     <clear />
-    <add key="AspNetCore" value="https://dotnet.myget.org/F/aspnetcore-ci-dev/api/v3/index.json" />
-    <add key="AspNetCoreTools" value="https://dotnet.myget.org/F/aspnetcore-tools/api/v3/index.json" />
-    <add key="NuGet" value="https://api.nuget.org/v3/index.json" />
   </packageSources>
 </configuration>

korebuild-lock.txt

@@ -1,2 +1,2 @@
-version:2.1.0-preview1-15576
-commithash:2f3856d2ba4f659fcb9253215b83946a06794a27
+version:2.1.0-preview1-15616
+commithash:ef83157a1e36c3efd0dd8498cde92611a64c34cc