sha3: change range statement in test to work with Go 1.3 and earlier

LGTM=bradfitz
R=agl, bradfitz
CC=golang-codereviews
https://golang.org/cl/157930043

sha3/sha3_test.go

@@ -183,7 +183,7 @@ func TestSqueezing(t *testing.T) {
 		d1 := newShakeHash()
 		d1.Write([]byte(testString))
 		var multiple []byte
-		for range ref {
+		for _ = range ref {
 			one := make([]byte, 1)
 			d1.Read(one)
 			multiple = append(multiple, one...)