[gnome-tweak-tool] ShellExtension: fix extension prefs button style

[Rui Matos <rtcm src gnome org>]

commit 616f2b3b274c5ff8f21dde27423a2c46a1d8b1bf
Author: Trinh Anh Ngoc <atw1990 gmail com>
Date:   Wed Feb 4 14:50:45 2015 +0700

    ShellExtension: fix extension prefs button style
    
    https://bugzilla.gnome.org/show_bug.cgi?id=743963

 gtweak/tweaks/tweak_group_shell_extensions.py |    6 +-----
 1 files changed, 1 insertions(+), 5 deletions(-)
---
diff --git a/gtweak/tweaks/tweak_group_shell_extensions.py b/gtweak/tweaks/tweak_group_shell_extensions.py
index ba82bf7..389ef7d 100644
--- a/gtweak/tweaks/tweak_group_shell_extensions.py
+++ b/gtweak/tweaks/tweak_group_shell_extensions.py
@@ -96,12 +96,8 @@ class _ShellExtensionTweak(Gtk.ListBoxRow, Tweak):
         if self._shell.SUPPORTS_EXTENSION_PREFS:
             prefs = os.path.join(ext['path'], "prefs.js")
             if os.path.exists(prefs):
-                icon = Gtk.Image()  
-                icon.set_from_icon_name("emblem-system-symbolic", Gtk.IconSize.BUTTON)
-                btn = Gtk.Button()
-                btn.props.vexpand = False
+                btn = Gtk.Button.new_from_icon_name("emblem-system-symbolic", Gtk.IconSize.BUTTON)
                 btn.props.valign = Gtk.Align.CENTER
-                btn.add(icon)
                 btn.connect("clicked", self._on_configure_clicked, uuid)
                 self.hbox.pack_start(btn, False, False, 0)