Add serde feature to database crate's chrono dependency

The feature was already used by another crate in the workspace, so the
database crate would build with `cargo build`, but not with `cargo build
-p database`. This fixes that.

Author: tgnottingham

database/Cargo.toml

@@ -15,7 +15,7 @@ async-trait = "0.1"
 tokio = { version = "1.6", features = ["sync", "macros"] }
 snap = "1"
 intern = { path = "../intern" }
-chrono = "0.4"
+chrono = { version = "0.4", features = ["serde"] }
 reqwest = { version = "0.11", features = ["blocking"] }
 postgres-native-tls = "0.5"
 native-tls = "0.2"