Fix the expected output for test_set_serializer.

tests/test_set_serializer.expected

@@ -9,4 +9,4 @@ my_object.to_string(custom serializer)=Custom Output
 Next line of output should be from the custom freeit function:
 freeit, value=123
 Check that the custom serializer does not include nul byte:
-my_object.to_string(custom serializer)={"double":                                                                                                                            1.}
+my_object.to_string(custom serializer)={"double":                                                                                                                            1}