Fix avatar at the bottom of commenting form.

Use the common Comments.avatar method to generate the <img> tag,
giving us the same default avatar that we use everywhere.

template/app/view/comments/Form.js

@@ -32,8 +32,7 @@ Ext.define('Docs.view.comments.Form', {
             '</tpl>',
             '<textarea>{content}</textarea>',
             '<div class="com-meta">',
-                '<img class="avatar" width="25" height="25"',
-                    ' src="http://www.gravatar.com/avatar/{user.emailHash}?s=25&amp;r=PG&amp;d=http://www.sencha.com/img/avatar.png">',
+                '{[Docs.Comments.avatar(values.user.emailHash)]}',
                 '<div class="form-author">Logged in as {user.userName}</div>',
                 '<tpl if="!updateComment">',
                     '<label class="subscribe">',