doc: fix typo in go_for_cpp_programmers.html

R=rsc, gri
CC=golang-dev
https://golang.org/cl/2191043

doc/go_for_cpp_programmers.html

@@ -668,7 +668,7 @@ func manager(ch chan cmd) {
 	var val int = 0
 	for {
 		c := <- ch
-		if c.get { c.val = val ch <- c }
+		if c.get { c.val = val; ch <- c }
 		else { val = c.val }
 	}
 }