chore: update rust edition to 2021 (#332)

marcoieni · web-flow · commit e4e6ac2859b5 · 2023-12-23T05:30:19.000+01:00
diff --git a/book.toml b/book.toml
@@ -14,7 +14,7 @@ extra-watch-dirs = ["po", "third_party"]
 after = ["links"]
 
 [rust]
-edition = "2018"
+edition = "2021"
 
 [output.html]
 curly-quotes = true
