Default all examples to 2021 edition.

mattheww · mattheww · commit 2abadebb8cfc · 2022-01-01T16:25:33.000Z
diff --git a/book.toml b/book.toml
@@ -11,4 +11,4 @@ git-repository-url = "https://github.com/rust-lang/reference/"
 "/expressions/enum-variant-expr.html" = "struct-expr.html"
 
 [rust]
-edition = "2018"
+edition = "2021"
