runtime: soften up hash checks a bit

The hash tests generate occasional failures, quiet them some more.

In particular we can get 1 collision when the expected number is
.001 or so. That shouldn't be a dealbreaker.

Fixes #12311

Change-Id: I784e91b5d21f4f1f166dc51bde2d1cd3a7a3bfea
Reviewed-on: https://go-review.googlesource.com/13902Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>

src/runtime/hash_test.go

@@ -74,7 +74,7 @@ func (s *HashSet) check(t *testing.T) {
 	pairs := int64(s.n) * int64(s.n-1) / 2
 	expected := float64(pairs) / math.Pow(2.0, float64(hashSize))
 	stddev := math.Sqrt(expected)
-	if float64(collisions) > expected+SLOP*3*stddev {
+	if float64(collisions) > expected+SLOP*(3*stddev+1) {
 		t.Errorf("unexpected number of collisions: got=%d mean=%f stddev=%f", collisions, expected, stddev)
 	}
 }