Zxcvbn-rs-py

- Upgrade dependencies and fix linter warnings

- Upgrade `derive_builder` to 0.5.0
- Fix a bug that was causing incorrect scoring for some passwords (https://github.com/shssoichiro/zxcvbn-rs/issues/13)

- [SEMVER_MAJOR] Change the signature for `zxcvbn` to take `&[]` instead of `Option<&[]>` for `user_inputs` (https://github.com/shssoichiro/zxcvbn-rs/issues/9)
- [SEMVER_MAJOR] Change the signature for `zxcvbn` to return `Result<Entropy, ZxcvbnError>` instead of `Option<Entropy>` (https://github.com/shssoichiro/zxcvbn-rs/issues/11)

- Fix for a BC-breaking change in nightly Rust (https://github.com/shssoichiro/zxcvbn-rs/pull/8)
- Upgrade `serde` to 1.0
- Silence a warning from `derive_builder`

- Upgrade `itertools` to 0.6

- Upgrade to derive_builder 0.4