Update hbs_renderer.rs

Author: expikr

src/renderer/html_handlebars/hbs_renderer.rs

@@ -703,8 +703,8 @@ fn make_data(
         let mut theme = Vec::new();
         for name in &html_config.additional_theme {
             match name {
-                Ok(p) => theme.push(p.to_lowercase()),
-                Err(_) => theme.push(name.to_lowercase()),
+                Ok(p) => theme.push(p.to_str().to_lowercase()),
+                Err(_) => theme.push(name.to_str().to_lowercase()),
             }
         }
         data.insert("additional_theme".to_owned(), json!(theme));