fix: fix export row_index error

lib/tallty_import_export/export.rb

@@ -100,8 +100,8 @@ module TalltyImportExport
             [association_record]
 
           records.each do |record|
-            headers.each_with_index do |header, col_index|
             index += 1
+            headers.each_with_index do |header, col_index|
               _data = header[:source] ?
                 handle_data(association_record, header, index) :
                 handle_data(record, header, index)