Improve time formatting of log output

Previously, the time was formatted as ISO8601 timestamps which is
barely readable by humans. Activating the `chrono` feature allows
us to format with a different format string. The output now looks
like this:

2021-03-01 11:59:52  DEBUG Database and seed will be stored in /home/thomas/.local/share/xmr-btc-swap
2021-03-01 11:59:52  DEBUG Starting monero-wallet-rpc on port 40673
2021-03-01 11:59:59  DEBUG Still got 0.00009235 BTC left in wallet, swapping ...
2021-03-01 11:59:59  DEBUG Dialing alice at 12D3KooWCdMKjesXMJz1SiZ7HgotrxuqhQJbP5sgBm2BwP1cqThi
2021-03-01 11:59:59  DEBUG Requesting quote for 0.00008795 BTC

There is a double space after the time which is already fixed in
tracing-subscriber but not yet released.

See tokio-rs/tracing#1271.

swap/Cargo.toml

@@ -58,7 +58,7 @@ toml = "0.5"
 tracing = { version = "0.1", features = ["attributes"] }
 tracing-futures = { version = "0.2", features = ["std-future", "futures-03"] }
 tracing-log = "0.1"
-tracing-subscriber = { version = "0.2", default-features = false, features = ["fmt", "ansi", "env-filter"] }
+tracing-subscriber = { version = "0.2", default-features = false, features = ["fmt", "ansi", "env-filter", "chrono"] }
 url = { version = "2.1", features = ["serde"] }
 uuid = { version = "0.8", features = ["serde", "v4"] }
 void = "1"

swap/src/bin/swap_cli.rs

@@ -52,6 +52,9 @@ async fn main() -> Result<()> {
         .with_writer(std::io::stderr)
         .with_ansi(is_terminal)
         .with_target(false)
+        .with_timer(tracing_subscriber::fmt::time::ChronoLocal::with_format(
+            "%F %T".to_owned(),
+        ))
         .finish();
 
     tracing::subscriber::set_global_default(subscriber)?;