[goocanvasmm] Use the newer sigc::mem_fun() syntax.

[Murray Cumming <murrayc src gnome org>]

commit a8be1daa21827c1e4a22e7b6bb5808bd1f08c97b
Author: Murray Cumming <murrayc murrayc com>
Date:   Fri Dec 16 11:58:09 2016 +0100

    Use the newer sigc::mem_fun() syntax.

 examples/simple/examplewindow.cc |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/examples/simple/examplewindow.cc b/examples/simple/examplewindow.cc
index df745db..f2acdbc 100644
--- a/examples/simple/examplewindow.cc
+++ b/examples/simple/examplewindow.cc
@@ -43,7 +43,7 @@ ExampleWindow::ExampleWindow()
   rect->set_property("stroke_color", Glib::ustring("yellow"));
   rect->set_property("fill_color", Glib::ustring("red"));
 #endif //GLIBMM_PROPERTIES_ENABLED
-  rect->signal_button_press_event ().connect (sigc::mem_fun (this,
+  rect->signal_button_press_event ().connect (sigc::mem_fun(*this,
     &ExampleWindow::on_rect_button_press));
 
   auto text = Goocanvas::Text::create("Hello World", 300, 300, -1, Goocanvas::ANCHOR_CENTER);