Fix messagepack test and make Json default codec

Author: saulecabrera

src/lib.rs

@@ -10,10 +10,10 @@ pub use container::*;
 /// Supported input encoding.
 #[derive(Copy, Clone, Debug, PartialEq, Eq, PartialOrd, Ord, ValueEnum, Default)]
 pub enum Codec {
+    #[default]
     /// JSON input.
     Json,
     /// Raw input, no validation, passed as-is.
-    #[default]
     Raw,
     /// JSON input encoded as Messagepack.
     Messagepack,

tests/fixtures/build/messagepack-valid.wasm

@@ -3,5 +3,7 @@ use std::io::{Read, Write};
 fn main() {
     let mut buf: Vec<u8> = vec![];
     std::io::stdin().read_to_end(&mut buf).unwrap();
+    let mut cursor = std::io::Cursor::new(&buf);
+    rmpv::decode::read_value(&mut cursor).expect("Valid messagepack");
     std::io::stdout().write_all(&buf).unwrap();
 }