Auto merge of rust-lang#8476 - xFrednet:0000-update-edition-for-rustfmt, r=giraffate

Update edition in rustfmt.toml

I noticed that our `rustfmt.toml` still has the edition 2018 listed. This updates the configuration to use 2021.

This luckily doesn't introduce any formatting changes 🙃

changelog: none

Author: bors

rustfmt.toml

@@ -2,6 +2,6 @@ max_width = 120
 comment_width = 100
 match_block_trailing_comma = true
 wrap_comments = true
-edition = "2018"
+edition = "2021"
 error_on_line_overflow = true
 version = "Two"