add explicit restore step

azure-pipelines.ix.yml

@@ -42,6 +42,12 @@ steps:
 - script: nbgv cloud -p Ix.NET\Source
   displayName: Set Version
 
+- task: DotNetCoreCLI@2
+  inputs:
+    command: restore
+    projects: Ix.NET/Source/**/*.csproj 
+  displayName: Restore
+
 - task: DotNetCoreCLI@2
   inputs:
     command: pack