Resolve type_repetition_in_bounds clippy lint
Resolve type_repetition_in_bounds clippy lint

    error: this type has already been used as a bound predicate
       --> src/value/ser.rs:278:9
        |
    278 |         T: Display,
        |         ^^^^^^^^^^
        |
        = note: `-D clippy::type-repetition-in-bounds` implied by `-D clippy::pedantic`
        = help: consider combining the bounds: `T: Sized + Display`
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#type_repetition_in_bounds

    error: this type has already been used as a bound predicate
       --> src/value/ser.rs:611:9
        |
    611 |         T: Display,
        |         ^^^^^^^^^^
        |
        = help: consider combining the bounds: `T: Sized + Display`
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#type_repetition_in_bounds

serde-rs/json