Raise serde version to support no-std builds (#19)

Serde impls for Ip*Addr from serde 1.0.210 don't require std (if used
with rust>=1.77, which we require anyway).

Cargo.toml

@@ -27,7 +27,7 @@ serde = ["dep:serde"]
 
 [dependencies]
 bitstring = { version = "0.2.0", optional = true, features = ["net"] }
-serde = { version = "1.0.27", optional = true }
+serde = { version = "1.0.210", optional = true, default-features = false }
 
 [dev-dependencies]
 serde_test = "1.0.27"