Cleanup NuGet.config

Author: smitpatel

NuGet.config

@@ -1,7 +1,8 @@
 <?xml version="1.0" encoding="utf-8"?>
 <configuration>
   <packageSources>
-    <add key="AspNetCore" value="https://dotnet.myget.org/F/aspnetcore-ci-release/api/v3/index.json" />
-    <add key="NuGet" value="https://nuget.org/api/v2/" />
+    <clear />
+    <add key="AspNetCore" value="https://dotnet.myget.org/F/aspnetcore-master/api/v3/index.json" />
+    <add key="NuGet" value="https://api.nuget.org/v3/index.json" />
   </packageSources>
 </configuration>