ssh-key: bump ed25519-dalek to v3.0.0-pre.7 (#508)

Also loosens the `=` restriction since this crate is prctically finished

Author: tarcieri

Cargo.lock

@@ -39,7 +39,7 @@ zeroize = { version = "1", default-features = false }
 argon2 = { version = "0.6.0-rc.8", optional = true, default-features = false, features = ["alloc"] }
 bcrypt-pbkdf = { version = "0.11", optional = true, default-features = false, features = ["alloc"] }
 dsa = { version = "0.7.0-rc.14", optional = true, default-features = false, features = ["hazmat"] }
-ed25519-dalek = { version = "=3.0.0-pre.6", optional = true, default-features = false }
+ed25519-dalek = { version = "3.0.0-pre.7", optional = true, default-features = false }
 hex = { version = "0.4", optional = true, default-features = false, features = ["alloc"] }
 hmac = { version = "0.13.0-rc.5", optional = true }
 p256 = { version = "0.14.0-rc.9", optional = true, default-features = false, features = ["ecdsa"] }