doc: fix comment type typo

Fixes #9418

Change-Id: I044fa1d26d972f012f00388a84c4d0f143cf4f63
Reviewed-on: https://go-review.googlesource.com/1970Reviewed-by: Robert Griesemer <gri@golang.org>

doc/go_spec.html

 <!--{
 	"Title": "The Go Programming Language Specification",
-	"Subtitle": "Version of November 11, 2014",
+	"Subtitle": "Version of December 22, 2014",
 	"Path": "/ref/spec"
 }-->
 
@@ -1981,7 +1981,7 @@ with no explicit type.
 </p>
 
 <pre>
-var d = math.Sin(0.5)  // d is int64
+var d = math.Sin(0.5)  // d is float64
 var i = 42             // i is int
 var t, ok = x.(T)      // t is T, ok is bool
 var n = nil            // illegal