Update Cargo.toml , mimalloc speedup

By default this library builds mimalloc in secure mode. This means that heap allocations are encrypted, but this results in a 3% increase in overhead.

Cargo.toml

@@ -47,7 +47,7 @@ serde = { version = "1", features = ["derive"] }
 serde_json = "1"
 
 # malloc
-mimalloc = { version = "0.1", optional = true }
+mimalloc = { version = "0.1", optional = true, default-features = false }
 
 [target.'cfg(not(target_env = "msvc"))'.dependencies]
 jemallocator = { version = "0.5", optional = true }