[glibmm] Binding: Make a the TransformProp constructor explicit.

[Murray Cumming <murrayc src gnome org>]

commit 2fcbab6fbd14644e7005379cd6d716daefaef9b0
Author: Murray Cumming <murrayc murrayc com>
Date:   Mon Dec 12 10:37:58 2016 +0100

    Binding: Make a the TransformProp constructor explicit.

 glib/src/binding.hg |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/glib/src/binding.hg b/glib/src/binding.hg
index 730baad..db2baa1 100644
--- a/glib/src/binding.hg
+++ b/glib/src/binding.hg
@@ -396,7 +396,7 @@ private:
   public:
     using SlotTypedTransform = sigc::slot<bool(const T_from&, T_to&)>;
 
-    TransformProp(const SlotTypedTransform& slot) : typed_transform(slot) {}
+    explicit TransformProp(const SlotTypedTransform& slot) : typed_transform(slot) {}
 
     bool operator()(const GValue* from_value, GValue* to_value)
     {