Update rust edition to 2021 (#749)

* build: update rust edition 2021

* cargo: format all

* build: fix tests and warnings

config/Cargo.toml

@@ -7,7 +7,7 @@ license = "Apache-2.0"
 repository = "https://github.com/mimblewimble/grin-wallet"
 keywords = [ "crypto", "grin", "mimblewimble" ]
 workspace = ".."
-edition = "2018"
+edition = "2021"
 
 [dependencies]
 rand = "0.6"

config/src/config.rs

@@ -476,4 +476,4 @@ impl GlobalWalletConfig {
 			.replace("WARN", "Warning")
 			.replace("ERROR", "Error")
 	}
-}
+}