add optional to cargo.toml
@@ -28,7 +28,7 @@ chrono = "0.4.12"
hex = "0.4.2"
blake2 = "0.9"
paho-mqtt = { version = "0.9", optional = true }
-regex = "1.4"
+regex = { version = "1.4", optional = true }
tokio = { version = "1.1", features = ["macros", "sync", "rt-multi-thread"] }
thiserror = "1.0"
num_cpus = "1.13"
