Sanitize directory name as a key

lib/jekyll/readers/data_reader.rb

@@ -38,7 +38,7 @@ module Jekyll
         next if @entry_filter.symlink?(path)
 
         if File.directory?(path)
-          read_data_to(path, data[entry] = {})
+          read_data_to(path, data[sanitize_filename(entry)] = {})
         else
           key = sanitize_filename(File.basename(entry, ".*"))
           data[key] = read_data_file(path)

test/test_site.rb

@@ -446,9 +446,9 @@ class TestSite < JekyllUnitTest
           source_dir, "_data", "categories.01", "dairy.yaml"
         ))
 
-        assert_equal site.data["categories.01"]["dairy"], file_content
+        assert_equal site.data["categories01"]["dairy"], file_content
         assert_equal(
-          site.site_payload["site"]["data"]["categories.01"]["dairy"],
+          site.site_payload["site"]["data"]["categories01"]["dairy"],
           file_content
         )
       end