Upgrade to jwalk 0.5

[Byron]

Also see if the new feature, client state, can be leveraged.

see Byron/jwalk#7 (comment)

[Byron]

There seems to be a performance regression. To reproduce, do the following:

git clone https://github.com/Byron/dua-cli && \
cd dua-cli && \
git checkout 4990fa4202f2b687ee2476efe0a406fdfe23fd96 && \
cargo run --release -- i ~/

Watch the CPU usage - it starts out using many cores, but quickly degrades to just a single core, as if work stealing doesn't work anymore or works differently.

Compare that to the latest master, which uses jwalk 0.4.0.