fix: symbolize_keys

lib/tallty_import_export/export.rb

@@ -150,7 +150,7 @@ module TalltyImportExport
     end
 
     def process_options(options = {})
-      options = export_options.merge(options).with_indifferent_access
+      options = export_options.merge(options).with_indifferent_access.symbolize_keys
 
       @row_height ||= options.delete(:row_height) || 25
       @width ||= (options.delete(:width) || 20).to_f