Bump crate edition to 2021

Author: tnull

Cargo.toml

@@ -2,7 +2,7 @@
 name = "lightning-liquidity"
 version = "0.1.0"
 authors = ["John Cantrell <[email protected]>", "Elias Rohrer <[email protected]>"]
-edition = "2018"
+edition = "2021"
 description = "Types and primitives to integrate a spec-compliant LSP with an LDK-based node."
 
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html