Fix namespace

src/lib/DataStructures/Catalogue.vala

@@ -1,6 +1,4 @@
-using Invercargill.DataStructures;
-
-namespace Invercargill {
+namespace Invercargill.DataStructures {
 
     public class Catalogue<TKey, TValue> : Enumerable<Grouping<TKey, TValue>>, Lot<Grouping<TKey, TValue>>, ReadOnlyCategoryIndex<TKey, TValue>, CategoryIndex<TKey, TValue> {