Fix deprecation warnings about SipHasher vs DefaultHasher

[rozbb]

Currently, building gives the warning messages:

warning: use of deprecated item: use `std::collections::hash_map::DefaultHasher` instead, #[warn(deprecated)] on by default
    --> src/int.rs:4442:30
     |
4442 |             let mut hasher = std::hash::SipHasher::new();
     |                              ^^^^^^^^^^^^^^^^^^^^^^^^^

warning: use of deprecated item: use `std::collections::hash_map::DefaultHasher` instead, #[warn(deprecated)] on by default
    --> src/int.rs:4442:30
     |
4442 |             let mut hasher = std::hash::SipHasher::new();
     |                              ^^^^^^^^^^^^^^^^^^^^^^^^^

warning: use of deprecated item: use `std::collections::hash_map::DefaultHasher` instead, #[warn(deprecated)] on by default
    --> src/int.rs:4446:30
     |
4446 |             let mut hasher = std::hash::SipHasher::new();
     |                              ^^^^^^^^^^^^^^^^^^^^^^^^^

warning: use of deprecated item: use `std::collections::hash_map::DefaultHasher` instead, #[warn(deprecated)] on by default
    --> src/int.rs:4446:30
     |
4446 |             let mut hasher = std::hash::SipHasher::new();
     |                              ^^^^^^^^^^^^^^^^^^^^^^^^^

    Finished release [optimized] target(s) in 94.5 secs
     Running target/release/deps/quickcheck-5d65a93dfbfec02c