Depend on chrono version 0.4.23 or higher

We have seen cases where, with chrono versions lower than 0.4.23, the
program fails to build because for one reason or another the
with_ymd_and_hms method is not available on the Tz type.
Play it safe and depend on version 0.4.23 to prevent such issues from
happening again.

Cargo.toml

@@ -43,7 +43,7 @@ grev = {version = "0.1.3"}
 [dependencies]
 apca = {version = "0.26.2"}
 anyhow = {version = "1.0", default-features = false, features = ["std"]}
-chrono = {version = "0.4", default-features = false}
+chrono = {version = "0.4.23", default-features = false}
 chrono-tz = {version = "0.8.1", default-features = false, features = ["std"]}
 clap = { version = "3.1.18", features = ["derive"] }
 clap_complete = { version = "3.1.4", optional = true }