Explicitly depend on serde's derive feature

This feature is explicitly enabled via the ron dev dependency. This is
cargo bug rust-lang/cargo#7916

This was reported on URLO
https://users.rust-lang.org/t/serde-hashmap-serialization-key-error/49776/5

CHANGELOG.md

@@ -7,6 +7,12 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 ## [Unreleased]
 
+### Fixed
+
+* Depend on serde with the `derive` feature enabled.
+    The `derive` feature is required to deserliaze untagged enums which are used in the `DefaultOnError` helpers.
+    This fixes compilation of `serde_with` in scenarios where no other crate enables the `derive` feature.
+
 ## [1.5.0]
 
 ### Added

Cargo.toml

@@ -35,7 +35,7 @@ macros = ["serde_with_macros"]
 chrono_crate = {package = "chrono", version = "0.4.1", features = ["serde"], optional = true}
 doc-comment = {version = "0.3.3", optional = true}
 hex = {version = "0.4.2", optional = true}
-serde = "1.0.75"
+serde = {version = "1.0.75", features = ["derive"]}
 serde_json = {version = "1.0.1", optional = true}
 serde_with_macros = {path = "./serde_with_macros", version = "1.2.0", optional = true}