Fix unstable book

diff --git a/src/doc/unstable-book/src/language-features/macro-at-most-once-rep.md b/src/doc/unstable-book/src/language-features/macro-at-most-once-rep.md
index dbaf91b6e78b2a1236bf5f6853a864571c5d219d..ec9d85db107d4b08418311d10117d249efd983af 100644 (file)
--- a/src/doc/unstable-book/src/language-features/macro-at-most-once-rep.md
+++ b/src/doc/unstable-book/src/language-features/macro-at-most-once-rep.md
@@ -6,7 +6,10 @@ With this feature gate enabled, one can use `?` as a Kleene operator meaning "0
 or 1 repetitions" in a macro definition. Previously only `+` and `*` were allowed.
 
 For example:
+
 ```rust
+#![feature(macro_at_most_once_rep)]
+
 macro_rules! foo {
     (something $(,)?) // `?` indicates `,` is "optional"...
         => {}