Fix duplicates in tab complete

src/de/steamwar/command/AbstractSWCommand.java

@@ -93,6 +93,7 @@ public abstract class AbstractSWCommand<T> {
                 .flatMap(Collection::stream)
                 .filter(s -> !s.isEmpty())
                 .filter(s -> s.toLowerCase().startsWith(string))
+                .distinct()
                 .collect(Collectors.toList());
     }