minor: bump linked_hash_map version (#197)

linked_hash_map had unsoundness issues in <= 0.5.2

Author: Dylan-DPC

Cargo.toml

@@ -32,7 +32,7 @@ rand = "0.7"
 serde = { version = "1.0", features = ["derive"] }
 serde_json = { version = "1.0", features = ["preserve_order"] }
 time = "0.1"
-linked-hash-map = "0.5"
+linked-hash-map = "0.5.3"
 hex = "0.4.2"
 md5 = "0.7.0"
 decimal = { version = "2.0.4", default_features = false, optional = true }