error: this argument is a mutable reference, but not used mutably
   --> src/inflight.rs:145:29
    |
145 |     fn available(&self, cx: &mut Context<'_>) -> bool {
    |                             ^^^^^^^^^^^^^^^^ help: consider changing to: `&Context<'_>`
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#needless_pass_by_ref_mut
note: the lint level is defined here
   --> src/lib.rs:1:27
    |
1   | #![deny(rust_2018_idioms, warnings, unreachable_pub)]
    |                           ^^^^^^^^
    = note: `#[deny(clippy::needless_pass_by_ref_mut)]` implied by `#[deny(warnings)]`