Remove upper-bound on ahash dependency version

[AlexandreCassagne]

Commit f7e979a (fix ahash MSRV nonsense) locks down the version of ahash to <= 0.8.7

This breaks our build alongside actix-web v4.5.1 which calls for ahash 0.8.9.

I can see there are some more recent commits in ahash (main) but I do not understand the underlying issue well enough to determine if the bug was fixed there.

Can you link this issue to a blocking issue on ahash so we can un-pin the dependency again on this repo?

cc @tobz

[AlexandreCassagne]

It looks like this MSRV bump was rolled back in this PR
tkaitchuck/aHash#208

[tobz]

Oh neat. If the MSRV bump has been reverted as of ahash 0.8.8, then we can remove the range constraint and instead pin to 0.8.8.

[tobz]

Released in metrics@v0.22.2.

[AlexandreCassagne]

Thanks @tobz.