[geary] Update appstream to point to new screenshots on wiki.gnome.org.

[Michael Gratton <mjog src gnome org>]

commit 8a20a4592c7ebe451c9670c6ffcb7bcf6196bc09
Author: Michael James Gratton <mike vee net>
Date:   Mon Sep 25 18:49:40 2017 +1000

    Update appstream to point to new screenshots on wiki.gnome.org.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=770860

 desktop/org.gnome.Geary.appdata.xml.in |    9 +++++++--
 1 files changed, 7 insertions(+), 2 deletions(-)
---
diff --git a/desktop/org.gnome.Geary.appdata.xml.in b/desktop/org.gnome.Geary.appdata.xml.in
index 093e564..b68d0ce 100644
--- a/desktop/org.gnome.Geary.appdata.xml.in
+++ b/desktop/org.gnome.Geary.appdata.xml.in
@@ -32,8 +32,13 @@
   <url type="bugtracker">https://bugzilla.gnome.org/enter_bug.cgi?product=geary</url>
   <url type="donation">http://www.gnome.org/friends/</url>
   <screenshots>
-    <screenshot type="default">
-      <image>http://yorba.org/geary/geary.png</image>
+    <screenshot>
+      <_caption>Geary displaying a conversation</_caption>
+      <image type="default" width="1600" 
height="900">https://wiki.gnome.org/Apps/Geary?action=AttachFile&amp;do=get&amp;target=geary-conversation-0.12.png</image>
+    </screenshot>
+    <screenshot>
+      <_caption>Geary showing the rich text composer</_caption>
+      <image type="source" width="1600" 
height="900">https://wiki.gnome.org/Apps/Geary?action=AttachFile&amp;do=get&amp;target=geary-composer-0.12.png</image>
     </screenshot>
   </screenshots>
   <translation type="gettext">geary</translation>