Downgrade ahash for wasm build

[samsamai]

When running ./build_web.sh, I ran into the following errors:

error: target is not supported, for more information see: https://docs.rs/getrandom/#unsupported-targets
   --> /Users/sss/.cargo/registry/src/git.luolix.top-1ecc6299db9ec823/getrandom-0.2.0/src/lib.rs:224:9
    |
224 | /         compile_error!("target is not supported, for more information see: \
225 | |                         https://docs.rs/getrandom/#unsupported-targets");
    | |_________________________________________________________________________^

error[E0433]: failed to resolve: use of undeclared type or module `imp`
   --> /Users/sss/.cargo/registry/src/git.luolix.top-1ecc6299db9ec823/getrandom-0.2.0/src/lib.rs:246:5
    |
246 |     imp::getrandom_inner(dest)
    |     ^^^ use of undeclared type or module `imp`

error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0433`.
error: could not compile `getrandom`.

To learn more, run the command again with --verbose.
warning: build failed, waiting for other jobs to finish...
error: build failed

Seems like getrandom doesn't see wasm32-unknown-unknown as a valid target.
Dropping ahash, which has the getrandom dependency, to version 0.4.6 fixes this for now.

[emilk]

Thanks for noticing this!

Seems to me like two other things should also happen:

• Open an issue for ahash
• Run the web build on the CI so this doesn't happen again

I have also been thinking about making ahash an optional dependency (I only use it for a speed boost anyway).... just me thinking out loud :)

[emilk]

Please add a comment to Cargo.toml about why we aren't using the latest ahash version (maybe link to this PR)

[emilk]

Issue filed to tkaitchuck/aHash#59

[emilk]

Upgraded to ahash 0.5 in 8393d1d