Housekeeping: change cake script to use new recipe location.

Author: glennawatson

build.cake

@@ -1,4 +1,5 @@
-#load nuget:https://www.myget.org/F/reactiveui?package=ReactiveUI.Cake.Recipe&prerelease
+#load nuget:https://pkgs.dev.azure.com/dotnet/ReactiveUI/_packaging/ReactiveUI/nuget/v3/index.json?package=ReactiveUI.Cake.Recipe&prerelease
+
 
 Environment.SetVariableNames();