ssh-key: bump dsa dependency to v0.7 release (#571)

Release PR: RustCrypto/signatures#1407

Author: tarcieri

Cargo.lock

@@ -28,7 +28,7 @@ zeroize = { version = "1.9", default-features = false }
 # optional dependencies
 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.16", optional = true, default-features = false, features = ["hazmat"] }
+dsa = { version = "0.7", optional = true, default-features = false, features = ["hazmat"] }
 ed25519-dalek = { version = "3.0.0-rc.1", optional = true, default-features = false }
 hex = { version = "0.4", optional = true, default-features = false, features = ["alloc"] }
 hmac = { version = "0.13", optional = true }