Depends on sized-chunks which has soundness problems

[mzabaluev]

cargo audit reports the following when im-rs 15.0.0 is in the dependency tree:

ID:       RUSTSEC-2020-0041
Crate:    sized-chunks
Version:  0.6.2
Date:     2020-09-06
URL:      https://rustsec.org/advisories/RUSTSEC-2020-0041
Title:    Multiple soundness issues in Chunk and InlineArray
Solution:  No safe upgrade is available!
Dependency tree: 
sized-chunks 0.6.2
└── im-rc 15.0.0

See bodil/sized-chunks#11

[brightly-salty]

An update: looks like this can be fixed by upgrading sized-chunks to 0.6.3. Would a PR be accepted?

[brightly-salty]

Looks like #179 already fixes this and updates sized-chunks to 0.6.4, so I will not create a new PR