Rust 2021 edition and bump spin

Author: jiegec

Cargo.toml

@@ -7,7 +7,7 @@ repository = "https://github.com/rcore-os/buddy_system_allocator"
 keywords = ["allocator", "no_std", "heap"]
 version = "0.8.0"
 authors = ["Jiajie Chen <noc@jiegec.ac.cn>", "Vinay Chandra Dommeti <github@vinay.vc>"]
-edition = "2018"
+edition = "2021"
 license = "MIT"
 
 [features]
@@ -16,5 +16,5 @@ use_spin = ["spin"]
 const_fn = []
 
 [dependencies.spin]
-version = "0.7"
+version = "0.9.3"
 optional = true