Releases the following new versions after the `digest` v0.9 (MSRV 1.41+)
and 2018 edition upgrade:

- `groestl` v0.9.0
- `md2` v0.9.0
- `md4` v0.9.0
- `ripemd320` v0.9.0
- `whirlpool` v0.9.0