math/big: simplify bool expression

Change-Id: I280c53be455f2fe0474ad577c0f7b7908a4eccb2
Reviewed-on: https://go-review.googlesource.com/36993Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/math/big/int.go

@@ -570,7 +570,7 @@ func (z *Int) binaryGCD(a, b *Int) *Int {
 // Rand sets z to a pseudo-random number in [0, n) and returns z.
 func (z *Int) Rand(rnd *rand.Rand, n *Int) *Int {
 	z.neg = false
-	if n.neg == true || len(n.abs) == 0 {
+	if n.neg || len(n.abs) == 0 {
 		z.abs = nil
 		return z
 	}