eliminate the warnings

[bud-adamas]

if there is no dyn, there are warnings like this:

    warning: trait objects without an explicit `dyn` are deprecated
    --> xxx.rs:5:45
    |
    5 | type Result<T> = std::result::Result<T, Box<error::Error>>;
    |                                             ^^^^^^^^^^^^ help: use `dyn`: `dyn error::Error`
    |
    = note: `#[warn(bare_trait_objects)]` on by default

    warning: trait objects without an explicit `dyn` are deprecated
    --> xxx.rs:21:32
    |
    21 |     fn cause(&self) -> Option<&error::Error> {
    |                                ^^^^^^^^^^^^ help: use `dyn`: `dyn error::Error`

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @marioidival (or someone else) soon.

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[marioidival]

@bud-adamas thank you!