[polari] joinDialog: Fix back button alignment

[Florian Müllner <fmuellner src gnome org>]

commit 70d7daf6cec67ba900966c1f1e675e35c2d51876
Author: Florian Müllner <fmuellner gnome org>
Date:   Tue Dec 22 18:34:29 2015 +0100

    joinDialog: Fix back button alignment
    
    We don't want the button to fill the available height ...

 src/joinDialog.js |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)
---
diff --git a/src/joinDialog.js b/src/joinDialog.js
index 51cd644..61308c1 100644
--- a/src/joinDialog.js
+++ b/src/joinDialog.js
@@ -89,7 +89,8 @@ const JoinDialog = new Lang.Class({
             }));
 
         let icon = new Gtk.Image({ icon_name: 'go-previous-symbolic' });
-        this._backButton = new Gtk.Button({ image: icon });
+        this._backButton = new Gtk.Button({ image: icon,
+                                            valign: Gtk.Align.CENTER });
         this._backButton.connect('clicked', Lang.bind(this,
             function() {
                 this._setPage(DialogPage.MAIN);