spec: use consistent quoting style in prose

Fixes #23389.

Change-Id: Id6e86eebe44809db12a0e14014c474bf4fbf5108
Reviewed-on: https://go-review.googlesource.com/87035Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

doc/go_spec.html

 <!--{
 	"Title": "The Go Programming Language Specification",
-	"Subtitle": "Version of January 3, 2018",
+	"Subtitle": "Version of January 9, 2018",
 	"Path": "/ref/spec"
 }-->
 
@@ -3619,7 +3619,7 @@ For unsigned integer values, the operations <code>+</code>,
 computed modulo 2<sup><i>n</i></sup>, where <i>n</i> is the bit width of
 the <a href="#Numeric_types">unsigned integer</a>'s type.
 Loosely speaking, these unsigned integer operations
-discard high bits upon overflow, and programs may rely on ``wrap around''.
+discard high bits upon overflow, and programs may rely on "wrap around".
 </p>
 <p>
 For signed integers, the operations <code>+</code>,