client: Enable std feature in types crate

The `client` is std only but we don't enable the `std` feature in
`types` - this is a bug.

Fix: rust-bitcoin#97

Author: tcharding

client/Cargo.toml

@@ -22,7 +22,7 @@ client-sync = ["jsonrpc"]
 
 [dependencies]
 bitcoin = { version = "0.32.0", default-features = false, features = ["std", "serde"] }
-types = { package = "corepc-types", version = "0.6.0", default-features = false, features = [] }
+types = { package = "corepc-types", version = "0.6.0", default-features = false, features = ["std"] }
 log = "0.4"
 serde = { version = "1.0.103", default-features = false, features = [ "derive", "alloc" ] }
 serde_json = { version = "1.0.117" }