[gtkmm-documentation] C++14: Use std::make_unique<>().

[Murray Cumming <murrayc src gnome org>]

commit eb6e286228f466147c1ee9144d03f189d03d7707
Author: Murray Cumming <murrayc murrayc com>
Date:   Wed Jul 6 14:34:22 2016 +0200

    C++14: Use std::make_unique<>().

 .../others/cellrenderercustom/cellrendererpopup.cc |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/examples/others/cellrenderercustom/cellrendererpopup.cc 
b/examples/others/cellrenderercustom/cellrendererpopup.cc
index 57d6f9b..3f4838a 100644
--- a/examples/others/cellrenderercustom/cellrendererpopup.cc
+++ b/examples/others/cellrenderercustom/cellrendererpopup.cc
@@ -127,7 +127,7 @@ Gtk::CellEditable* CellRendererPopup::start_editing_vfunc(GdkEvent*,
   if(!property_editable())
     return nullptr;
 
-  std::unique_ptr<PopupEntry> popup_entry (new PopupEntry(path));
+  auto popup_entry = std::make_unique<PopupEntry>(path));
 
   popup_entry->signal_editing_done ().connect(sigc::mem_fun(*this, &Self::on_popup_editing_done));
   popup_entry->signal_arrow_clicked().connect(sigc::mem_fun(*this, &Self::on_popup_arrow_clicked));