Upgrade ahash

[brson]

This avoids a compile error from the nightly removal of the stdsimd feature:

$ cargo test
warning: `/home/brian/dada/.cargo/config` is deprecated in favor of `config.toml`
note: if you need to support cargo 1.38 or earlier, you can symlink `config` to `config.toml`
   Compiling ahash v0.7.6
   Compiling crossbeam-channel v0.5.8
error[E0635]: unknown feature `stdsimd`
  --> /home/brian/.cargo/registry/src/index.crates.io-6f17d22bba15001f/ahash-0.7.6/src/lib.rs:33:42
   |
33 | #![cfg_attr(feature = "stdsimd", feature(stdsimd))]
   |                                          ^^^^^^^

For more information about this error, try `rustc --explain E0635`.
error: could not compile `ahash` (lib) due to 1 previous error
warning: build failed, waiting for other jobs to finish...

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[brson]

The failure is some fresh nightly clippy stuff. I'm ignoring it for now.