Update edition value

Author: Conor Okus

examples/bitcoind-rpc-client/Cargo.toml

@@ -3,7 +3,7 @@ name = "bitcoind-rpc-client"
 version = "0.1.0"
 authors = ["Conor Okus <conor@squarecrypto.org>"]
 license = "MIT OR Apache-2.0"
-edition = "2021"
+edition = "2018"
 
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html