crypto/secp256k1: Fix invalid document link (#18297)

crypto/secp256k1/curve.go

@@ -310,7 +310,7 @@ var theCurve = new(BitCurve)
 func init() {
 	// See SEC 2 section 2.7.1
 	// curve parameters taken from:
-	// http://www.secg.org/collateral/sec2_final.pdf
+	// http://www.secg.org/sec2-v2.pdf
 	theCurve.P, _ = new(big.Int).SetString("0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEFFFFFC2F", 0)
 	theCurve.N, _ = new(big.Int).SetString("0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEBAAEDCE6AF48A03BBFD25E8CD0364141", 0)
 	theCurve.B, _ = new(big.Int).SetString("0x0000000000000000000000000000000000000000000000000000000000000007", 0)