Update app.py

app.py

@@ -27,7 +27,7 @@ nodename_to_protoIDs = defaultdict()
 
 for species, imgpath in species_to_imgpath.items():
     for foldername in os.listdir(imgpath):
-        if os.isdir(os.path.join(imgpath, foldername)):
+        if os.path.isdir(os.path.join(imgpath, foldername)):
             folderpath = os.path.join(imgpath, foldername)
             for filename in os.listdir(folderpath):
                 if filename.endswith('png') or filename.endswith('jpg'):