Bump to pre-releases

[baloo]

• password-hash =0.6.0-pre.0
• digest =0.11.0-pre.8
• curve25519-dalek =4.2.0-pre
• scrypt =0.12.0-pre.0
• sha1 =0.11.0-pre.3
• sha2 =0.11.0-pre.3
• hkdf =0.13.0-pre.3

[baloo]

I'll need to bump MSRV, I'll let CI figure those ones out for me.