Bump bzip2 to 0.6 for new rust backend

[RagnarGrootKoerkamp]

I ran into some issues trying to run a binary compiled on my laptop on a server, and it turns out that this is because the server is missing the libbz2.so.1.0 file that is dynamically linked against.

The current bzip2 0.4 dependency tries to dynamically link against bz2, and falls back to building from source.
One fix would be to simply add the static feature (possibly only enabled via some feature like static-bzip2 on needletail), but the simpler fix is probably to just bump it to the current 0.6 as I did here, since it now uses the rust backend by default, which should just fix all these issues completely.

Note that some other crates/compression backends also have breaking updates, but it may not be desirable to bump those, because eg linking to lib-zma 0.3.13 and 0.4.5 at the same time is impossible.
This is not an issue for bzip2, because the new version does not link against anything anymore.

[RagnarGrootKoerkamp]

Thanks! Could you also do a crates.io release (in case this is not already pending)?

[audy]

Thanks @RagnarGrootKoerkamp! Just pushed to crates.io