[glibmm] resolver example: Use std::strtoul instead of strtoul.

[Murray Cumming <murrayc src gnome org>]

commit db071c425d89bb1eca205546ef5cdae6d6dc3a1f
Author: Murray Cumming <murrayc murrayc com>
Date:   Tue Sep 1 12:26:30 2015 +0200

    resolver example: Use std::strtoul instead of strtoul.

 examples/network/resolver.cc |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/examples/network/resolver.cc b/examples/network/resolver.cc
index 42f36a6..c8506f2 100644
--- a/examples/network/resolver.cc
+++ b/examples/network/resolver.cc
@@ -401,7 +401,7 @@ do_connectable (const std::string& arg, gboolean synchronous)
         {
             host = arg.substr (0, pos);
             port_str = arg.substr(pos);
-            port = strtoul (port_str.c_str (), nullptr, 10);
+            port = std::strtoul (port_str.c_str (), nullptr, 10);
         }
         else
             port = 0;