Bump version for 0.21.0 release (#596)

Author: sholderbach

Cargo.lock

@@ -6,7 +6,7 @@ license = "MIT"
 name = "reedline"
 repository = "https://github.com/nushell/reedline"
 rust-version = "1.62.1"
-version = "0.20.0"
+version = "0.21.0"
 
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 [lib]