[glibmm] Examples: Use nullptr instead of 0.

[Murray Cumming <murrayc src gnome org>]

commit f49998f7252464c28d7b558ea7dca4fcfddca3d7
Author: Murray Cumming <murrayc murrayc com>
Date:   Fri Nov 20 10:11:04 2015 +0100

    Examples: Use nullptr instead of 0.

 examples/thread/dispatcher.cc |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/examples/thread/dispatcher.cc b/examples/thread/dispatcher.cc
index e58cb22..84868db 100644
--- a/examples/thread/dispatcher.cc
+++ b/examples/thread/dispatcher.cc
@@ -108,7 +108,7 @@ void ThreadProgress::launch()
 void ThreadProgress::join()
 {
   thread_->join();
-  thread_ = 0;
+  thread_ = nullptr;
 }
 
 bool ThreadProgress::unfinished() const