spec: remove an unnecessary semicolon from code example

Change-Id: Ie4c92da0e3cbb97d3d7e03c7d15196c34f58a2cd
Reviewed-on: https://go-review.googlesource.com/42613Reviewed-by: Robert Griesemer <gri@golang.org>

doc/go_spec.html

 <!--{
 	"Title": "The Go Programming Language Specification",
-	"Subtitle": "Version of April 28, 2017",
+	"Subtitle": "Version of May 3, 2017",
 	"Path": "/ref/spec"
 }-->
 
@@ -5126,7 +5126,7 @@ function completes.
 
 <pre>
 go Server()
-go func(ch chan&lt;- bool) { for { sleep(10); ch &lt;- true; }} (c)
+go func(ch chan&lt;- bool) { for { sleep(10); ch &lt;- true }} (c)
 </pre>