sys: update to edition 2021

Author: hhirtz

metis-sys/Cargo.toml

@@ -2,7 +2,7 @@
 name = "metis-sys"
 version = "0.1.1"
 authors = ["Hubert Hirtz <[email protected]>"]
-edition = "2018"
+edition = "2021"
 license = "MIT OR Apache-2.0"
 repository = "https://github.com/LIHPC-Computational-Geometry/metis-rs"
 documentation = "https://LIHPC-Computational-Geometry.github.io/metis-rs/metis_sys"