fix string to_s error

lib/tallty_import_export/export.rb

@@ -175,7 +175,7 @@ module TalltyImportExport
     def handle_format data, header
       case header[:attr_type].to_s
       when 'string'
-        date.to_s
+        data.to_s
       when 'datetime'
         data ? data.strftime('%F %H:%M') : nil
       when 'date'

lib/tallty_import_export/version.rb

 module TalltyImportExport
-  VERSION = "1.0.10"
+  VERSION = "1.0.11"
 end