Fix nuget package sources

NuGet.config

@@ -1,11 +1,10 @@
-<?xml version="1.0" encoding="utf-8"?>
+<?xml version="1.0" encoding="utf-8"?>
 <configuration>
   <packageRestore>
     <add key="enabled" value="True" />
     <add key="automatic" value="True" />
   </packageRestore>
   <packageSources>
-    <add key="monogame-dev" value="http://teamcity.monogame.net/guestAuth/app/nuget/v1/FeedService.svc/" />
-    <add key="nuget.org" value="https://www.nuget.org/api/v2/" />
+    <add key="nuget.org" value="https://api.nuget.org/v3/index.json" />
   </packageSources>
 </configuration>