Remove badges for draft versions of the book.

Author: ehuss

src/rust-2018/documentation/new-editions-of-the-book.md

@@ -1,11 +1,7 @@
 # New editions of the "the book"
 
-![Minimum Rust version: 1.18](https://img.shields.io/badge/Minimum%20Rust%20Version-1.18-red.svg) for drafts of the second edition
-
 ![Minimum Rust version: 1.26](https://img.shields.io/badge/Minimum%20Rust%20Version-1.26-brightgreen.svg) for the final version of the second edition
 
-![Minimum Rust version: 1.28](https://img.shields.io/badge/Minimum%20Rust%20Version-1.28-red.svg) for drafts of the 2018 edition
-
 ![Minimum Rust version: 1.31](https://img.shields.io/badge/Minimum%20Rust%20Version-1.31-brightgreen.svg) for the 2018 edition
 
 We've distributed a copy of "The Rust Programming Language," affectionately