math/big: fix typo in comment

Fixes #13875.

Change-Id: Icbb85c858d0bc545499a2b31622e9e7abdd7e5f9
Reviewed-on: https://go-review.googlesource.com/18441Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/math/big/int.go

@@ -273,7 +273,7 @@ func (z *Int) Mod(x, y *Int) *Int {
 // DivMod implements Euclidean division and modulus (unlike Go):
 //
 //	q = x div y  such that
-//	m = x - y*q  with 0 <= m < |q|
+//	m = x - y*q  with 0 <= m < |y|
 //
 // (See Raymond T. Boute, ``The Euclidean definition of the functions
 // div and mod''. ACM Transactions on Programming Languages and