Fixed leftover condition

src/main/java/cz/muni/fi/pv168/project/ui/action/task/ToggleCompletionAction.java

@@ -12,7 +12,7 @@ import java.util.List;
 public class ToggleCompletionAction<T extends ITask> extends AbstractAction<T> {
 
     public ToggleCompletionAction(ListHolder<T> listHolder, String description) {
-        super(listHolder, selectedRowsCount -> selectedRowsCount >= 1);
+        super(listHolder, selectedRowsCount -> selectedRowsCount == 1);
 
         putValue(NAME, "Toggle completion");
         putValue(SHORT_DESCRIPTION, description);