ssh-key: raise min serde version (#327)

Author: Eugeny

ssh-key/Cargo.toml

@@ -37,7 +37,7 @@ p521 = { version = "=0.14.0-pre.1", optional = true, default-features = false, f
 rand_core = { version = "0.6.4", optional = true, default-features = false }
 rsa = { version = "=0.10.0-pre.3", optional = true, default-features = false, features = ["sha2"] }
 sec1 = { version = "0.8.0-rc.3", optional = true, default-features = false, features = ["point"] }
-serde = { version = "1", optional = true }
+serde = { version = "1.0.16", optional = true }
 sha1 = { version = "=0.11.0-pre.4", optional = true, default-features = false }
 
 [dev-dependencies]