During upgrade to the Chromium 61 we have switched from GTK2 to GTK3
and now we have a few warnings about stuff being deprecated in GTK3.
Check any Linux build to get a list of them.

/cc @zcbenz 
atom/browser/ui/file_dialog_gtk.cc
public:
  FileChooserDialog(GtkFileChooserAction action,
                    const DialogSettings& settings)
      : parent_(static_cast<atom::NativeWindowViews*>(settings.parent_window)),
        filters_(settings.filters) {
    const char* confirm_text = GTK_STOCK_OK;
    if (!settings.button_label.empty())
      confirm_text = settings.button_label.c_str();
    else if (action == GTK_FILE_CHOOSER_ACTION_SAVE)
      confirm_text = GTK_STOCK_SAVE;
    else if (action == GTK_FILE_CHOOSER_ACTION_OPEN)
      confirm_text = GTK_STOCK_OPEN;
    dialog_ = gtk_file_chooser_dialog_new(
        settings.title.c_str(),
        NULL,
        action,
        GTK_STOCK_CANCEL, GTK_RESPONSE_CANCEL,