Update to Edition 2021

Author: michaellass

Cargo.toml

@@ -3,7 +3,7 @@ authors = ["Michael Lass <[email protected]>"]
 categories = ["data-structures", "memory-management"]
 description = "Allocate heap memory with user-specified alignment"
 documentation = "https://docs.rs/aligned_box/"
-edition = "2018"
+edition = "2021"
 homepage = "https://github.com/michaellass/aligned_box/"
 keywords = ["aligned", "alignment", "box", "heap", "memory"]
 license = "MIT"