query: mapQueryList avoid resizing new slice

This is a micro-optimization, but is a common call in Map. We know the final
size of neg, so we can just allocate that size.

Change-Id: I88ddc86889229557c218e33a86dce477e7b3fbed
diff --git a/query/query.go b/query/query.go
index dfce480..31741a0 100644
--- a/query/query.go
+++ b/query/query.go
@@ -260,9 +260,9 @@
 }
 
 func mapQueryList(qs []Q, f func(Q) Q) []Q {
-	var neg []Q
-	for _, sub := range qs {
-		neg = append(neg, Map(sub, f))
+	neg := make([]Q, len(qs))
+	for i, sub := range qs {
+		neg[i] = Map(sub, f)
 	}
 	return neg
 }