added avalonia-all feed to nuget.config

Author: Abdesol

nuget.config

@@ -2,6 +2,7 @@
 <configuration>
     <packageSources>
         <add key="nuget.org" value="https://api.nuget.org/v3/index.json" protocolVersion="3" />
+        <add key="AvaloniaCI" value="https://nuget.avaloniaui.net/repository/avalonia-nightly/index.json" />
         <add key="Aura.UI Myget" value="https://www.myget.org/F/auraui/api/v3/index.json" />
     </packageSources>
     <packageRestore>