Fixing typos in variable names.

app.py

@@ -91,7 +91,7 @@ def get_label_fractions(dataset):
                 f.write(json.dumps(label_counts))
     label_list = list(label_counts.keys())
     denom = sum(label_counts.values())
-    label_fractions = [label_counts[key]/denom for key in label_keys]
+    label_fractions = [label_counts[key]/denom for key in label_counts]
     return label_list, label_fractions