design/go2draft-contracts.md: fix result type of OrderedAbs.Abs

Change-Id: Iae77df84c1d4b2f3169f178bc76469f76c0b49bb
Reviewed-on: https://go-review.googlesource.com/c/proposal/+/212217
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
diff --git a/design/go2draft-contracts.md b/design/go2draft-contracts.md
index bd00879..7c43f65 100644
--- a/design/go2draft-contracts.md
+++ b/design/go2draft-contracts.md
@@ -2946,7 +2946,7 @@
 // ordered numeric types.
 type OrderedAbs(type T OrderedNumeric) T
 
-func (a OrderedAbs(T)) Abs() T {
+func (a OrderedAbs(T)) Abs() OrderedAbs(T) {
 	if a < 0 {
 		return -a
 	}