Make source maps work for assets in subdirectories

Author: DimitriosLisenko

lib/propshaft/compiler/source_mapping_urls.rb

@@ -11,7 +11,7 @@ def compile(asset, input)
 
   private
     def asset_path(source_mapping_url, logical_path)
-      source_mapping_url.gsub!(/^(.+\/)?#{url_prefix}\//, "")
+      source_mapping_url = ::File.basename(source_mapping_url)
 
       if logical_path.dirname.to_s == "."
         source_mapping_url