sort: Fix typo in stable sort comment

Fix `reverences`, which I believe should read as `references`.

Change-Id: I450efcbeee0f8861a84b209f2e6636764034232a
Reviewed-on: https://go-review.googlesource.com/19469Reviewed-by: Russ Cox <rsc@golang.org>

src/sort/sort.go

@@ -335,7 +335,7 @@ func StringsAreSorted(a []string) bool { return IsSorted(StringSlice(a)) }
 //    unstable or rely on enough different elements in each step to encode the
 //    performed block rearrangements. See also "In-Place Merging Algorithms",
 //    Denham Coates-Evely, Department of Computer Science, Kings College,
-//    January 2004 and the reverences in there.
+//    January 2004 and the references in there.
 //  - Often "optimal" algorithms are optimal in the number of assignments
 //    but Interface has only Swap as operation.