Update app.py

app.py

@@ -148,9 +148,9 @@ def image_to_wd14_tags(image: Image.Image, model_name: str, threshold: float,
         tag_outformat = tag
         if use_spaces:
             tag_outformat = tag_outformat.replace('_', ' ')
-            tag_outformat.replace(' ', '-')
+            tag_outformat = tag_outformat.replace(' ', '-')
         else:
-            tag_outformat.replace('_', '-')
+            tag_outformat = tag_outformat.replace('_', '-')
         if use_escape:
             tag_outformat = re.sub(RE_SPECIAL, r'\\\1', tag_outformat)
         if include_ranks: