property: add the necessary include file for std::function

This fixes the following error:

/home/aurel/devel/sigrok/pulseview/pv/prop/property.h:39:15: error: ‘function’ in namespace ‘std’ does not name a template type
  typedef std::function<GVariant* ()> Getter;

diff --git a/pv/prop/property.h b/pv/prop/property.h
index e5a523f93758ac6612f87637a06b7cad5770bd5e..b3aa1a690b00c3e29e74140317169bc5b2ac195e 100644 (file)
--- a/pv/prop/property.h
+++ b/pv/prop/property.h
@@ -23,6 +23,7 @@
 
 #include <glib.h>
 
+#include <functional>
 #include <QString>
 #include <QWidget>