Update payload.mdx

Author: reject-i

src/pages/sylvia/macros/attributes/payload.mdx

@@ -81,4 +81,4 @@ impl Contract {
 ```
 
 Sylvia uses the [`from_json`](https://docs.rs/cosmwasm-std/latest/cosmwasm_std/fn.from_json.html) to
-deserialize the `payload` field, so it has to be serialized do JSON.
+deserialize the `payload` field, so it has to be serialized to JSON.