Update build.yml

Author: Bertk

eng/build.yml

@@ -23,7 +23,7 @@ steps:
 - task: NuGetAuthenticate@1
   displayName: Authenticate with NuGet feeds
 
-- script: dotnet restore --configfile  $(Build.SourcesDirector)/nuget.config
+- script: dotnet restore --configfile nuget.config
   displayName: Restore packages
 
 - script: dotnet build -c $(BuildConfiguration) --no-restore -bl:build.msbuild.binlog