unicode: Fixed an out of date comment (MaxLatin1, not Latin1Max).

Change-Id: I3ca878e9685f650a9ff02aaac0e2e3cca89634c6
Reviewed-on: https://go-review.googlesource.com/4970Reviewed-by: Minux Ma <minux@golang.org>

src/unicode/graphic.go

@@ -82,7 +82,7 @@ func IsControl(r rune) bool {
 	if uint32(r) <= MaxLatin1 {
 		return properties[uint8(r)]&pC != 0
 	}
-	// All control characters are < Latin1Max.
+	// All control characters are < MaxLatin1.
 	return false
 }