[gnome-system-monitor] Add a missing tag to the AppData file

[Richard Hughes <rhughes src gnome org>]

commit 17b9d463b324b681c85d5bde04fee27714499ab2
Author: Richard Hughes <richard hughsie com>
Date:   Mon Jan 25 13:12:38 2016 +0000

    Add a missing tag to the AppData file

 gnome-system-monitor.appdata.xml.in |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)
---
diff --git a/gnome-system-monitor.appdata.xml.in b/gnome-system-monitor.appdata.xml.in
index 8acf733..dd891e0 100644
--- a/gnome-system-monitor.appdata.xml.in
+++ b/gnome-system-monitor.appdata.xml.in
@@ -27,6 +27,7 @@
   </screenshots>
   <url type="homepage">https://wiki.gnome.org/Apps/SystemMonitor</url>
   <updatecontact>robert.roth.off_at_gmail.com</updatecontact>
+  <project_group>GNOME</project_group>
 </application>