Gui: modernize C++: replace 'typedef' with 'using'

src/Gui/TaskElementColors.cpp

@@ -52,7 +52,7 @@ namespace bp = boost::placeholders;
 class ElementColors::Private: public Gui::SelectionGate
 {
 public:
-    typedef boost::signals2::connection Connection;
+    using Connection = boost::signals2::connection;
     std::unique_ptr<Ui_TaskElementColors> ui;
     ViewProviderDocumentObject *vp;
     ViewProviderDocumentObject *vpParent;