[gtk] Make color picker circular

[Matthias Clasen <matthiasc src gnome org>]

commit 4e868584057f0244645c2f14f4c964dc4343f5d7
Author: Matthias Clasen <mclasen redhat com>
Date:   Sat Aug 4 21:39:10 2018 -0400

    Make color picker circular
    
    The need for center alignment was pointed out by Timm Baeder.

 gtk/ui/gtkcoloreditor.ui | 2 ++
 1 file changed, 2 insertions(+)
---
diff --git a/gtk/ui/gtkcoloreditor.ui b/gtk/ui/gtkcoloreditor.ui
index 6840a276db..4f7f90a405 100644
--- a/gtk/ui/gtkcoloreditor.ui
+++ b/gtk/ui/gtkcoloreditor.ui
@@ -41,6 +41,8 @@
             <child>
               <object class="GtkButton" id="picker_button">
                 <property name="icon-name">color-select-symbolic</property>
+                <property name="halign">center</property>
+                <property name="valign">center</property>
                 <property name="tooltip-text" translatable="yes">Pick a color from the screen</property>
                 <signal name="clicked" handler="pick_color"/>
                 <style>