Fix for unicode strings in template map dynamic name

Fix for unicode strings with the dynamic part of template names.

For example, the following rule will export the file with a garbled name if the name contains Unicode strings.
```
"dist/blog/tags/{{tag.name}}.html" => {template_map, "src/templates/tag.html", {tag, PostsTagList}},
```
Sorry for missing it in the previous pull request.