Style Guide: Consistently delimit using `` pairs

Update the section discussing auto, to use `` delimiter pairs, and be
consistent with the comment style section below.

Change-Id: Ib175db1b97a426c66dbc27bdbcce31f680783baa
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2347304
Commit-Queue: Darwin Huang <huangdarwin@chromium.org>
Commit-Queue: Peter Kasting <pkasting@chromium.org>
Auto-Submit: Darwin Huang <huangdarwin@chromium.org>
Reviewed-by: Peter Kasting <pkasting@chromium.org>
Cr-Commit-Position: refs/heads/master@{#796535}

styleguide/c++/c++-dos-and-donts.md

@@ -227,8 +227,8 @@ Do not use `auto` when the type would be deduced to be a pointer type; this can
 cause confusion. Instead, specify the "pointer" part outside of `auto`:
 
 ```cpp
-auto item = new Item();  // BAD: auto deduces to Item*, type of |item| is Item*
-auto* item = new Item(); // GOOD: auto deduces to Item, type of |item| is Item*
+auto item = new Item();  // BAD: auto deduces to Item*, type of `item` is Item*
+auto* item = new Item(); // GOOD: auto deduces to Item, type of `item` is Item*
 ```
 
 ## Use `const` correctly