Adapt a use of 'latest edition'

Author: muzimuzhi

src/editions/index.md

@@ -6,7 +6,7 @@ However, there are times when it's useful to make backwards-incompatible changes
 
 If Rust had suddenly introduced these new keywords, some code would have broken: `let async = 1;` would no longer work.
 
-Rust uses **editions** to solve this problem. When there are backwards-incompatible changes, they are pushed into the next edition. Since editions are opt-in, existing crates won't use the changes unless they explicitly migrate into the new edition. For example, the latest version of Rust doesn't treat `async` as a keyword unless edition 2018 or later is chosen.
+Rust uses **editions** to solve this problem. When there are backwards-incompatible changes, they are pushed into the next edition. Since editions are opt-in, existing crates won't use the changes unless they explicitly migrate into the new edition. For example, the 2015 edition of Rust doesn't treat `async` as a keyword unless edition 2018 or later is chosen.
 
 Each crate chooses its edition [within its `Cargo.toml` file](https://doc.rust-lang.org/cargo/reference/manifest.html#the-edition-field). When creating a new crate with Cargo, it will automatically select the newest stable edition.