[gtkmm-documentation] Consistent spacing with lambdas.

[Murray Cumming <murrayc src gnome org>]

commit 299da7049a820052734029bd7da40b5800c97697
Author: Murray Cumming <murrayc murrayc com>
Date:   Mon Aug 24 00:06:27 2015 +0200

    Consistent spacing with lambdas.

 examples/book/listbox/examplewindow.cc |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/examples/book/listbox/examplewindow.cc b/examples/book/listbox/examplewindow.cc
index f4fb992..e984909 100644
--- a/examples/book/listbox/examplewindow.cc
+++ b/examples/book/listbox/examplewindow.cc
@@ -210,7 +210,7 @@ void ExampleWindow::on_sort_clicked()
 void ExampleWindow::on_reverse_sort_clicked()
 {
   m_ListBox.set_sort_func(
-    [](Gtk::ListBoxRow* row1, Gtk::ListBoxRow* row2)
+    [] (Gtk::ListBoxRow* row1, Gtk::ListBoxRow* row2)
     {
       return sort_func(row2, row1);
     });