Deprecation warnings when compiling tests of libserialize

[dgiagio]

There are some deprecation warnings when compiling tests of libserialize.

json.rs:2520:17: 2520:45 warning: use of deprecated item: call the .parse() method on the string instead, #[warn(deprecated)] on by default
json.rs:2520         assert!(::std::str::from_str::<Json>(s).unwrap() == from_str(s).unwrap());
                             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
<std macros>:1:1: 12:2 note: in expansion of assert!
json.rs:2520:9: 2520:83 note: expansion site
json.rs:3732:33: 3732:46 warning: use of deprecated item: call `.to_owned()` on `std::borrow::ToOwned` instead, #[warn(deprecated)] on by default
json.rs:3732             tree_map.insert("a".into_string(), U64(1));
                                             ^~~~~~~~~~~~~
json.rs:3733:33: 3733:46 warning: use of deprecated item: call `.to_owned()` on `std::borrow::ToOwned` instead, #[warn(deprecated)] on by default
json.rs:3733             tree_map.insert("b".into_string(), U64(2));
                                             ^~~~~~~~~~~~~
json.rs:3765:29: 3765:42 warning: use of deprecated item: call `.to_owned()` on `std::borrow::ToOwned` instead, #[warn(deprecated)] on by default
json.rs:3765         tree_map.insert("a".into_string(), 1u);
                                         ^~~~~~~~~~~~~
json.rs:3766:29: 3766:42 warning: use of deprecated item: call `.to_owned()` on `std::borrow::ToOwned` instead, #[warn(deprecated)] on by default
json.rs:3766         tree_map.insert("b".into_string(), 2);
                                         ^~~~~~~~~~~~~