Fix python errors on latest hack commits => make runserver happy again

uncloud/uncloud_pay/serializers.py

@@ -0,0 +1,12 @@
+from rest_framework import serializers
+from .models import Bill, Payment
+
+class BillSerializer(serializers.ModelSerializer):
+    class Meta:
+        model = Bill
+        fields = ['user', 'amount']
+
+class PaymentSerializer(serializers.ModelSerializer):
+    class Meta:
+        model = Payment
+        fields = ['user', 'amount', 'source', 'timestamp']