math/big: fix a duplicate "the" in a comment

Change-Id: Ib637381ab8a12aeb798576b781e1b3c458ba812d
GitHub-Last-Rev: 12994496b6b636d75564e5ae7e938b65bca526df
GitHub-Pull-Request: golang/go#34017
Reviewed-on: https://go-review.googlesource.com/c/go/+/192877Reviewed-by: Daniel Martí <mvdan@mvdan.cc>

src/math/big/ratconv.go

@@ -123,7 +123,7 @@ func (z *Rat) SetString(s string) (*Rat, bool) {
 	// Multiplications are commutative, so we can apply them in any
 	// order. We only have powers of 2 and 10, and we split powers
 	// of 10 into the product of the same powers of 2 and 5. This
-	// may reduce the the size of shift/multiplication factors or
+	// may reduce the size of shift/multiplication factors or
 	// divisors required to create the final fraction, depending
 	// on the actual floating-point value.