[fractal] snap: Added appstream to build packages, required for metainfo

[Ken VanDine <kvandine src gnome org>]

commit ad45b02084658717a5f0161f3d97d0d15ca7b1fc
Author: Ken VanDine <ken vandine canonical com>
Date:   Fri Jun 5 11:57:12 2020 -0400

    snap: Added appstream to build packages, required for metainfo

 build-aux/snap/snapcraft.yaml | 1 +
 1 file changed, 1 insertion(+)
---
diff --git a/build-aux/snap/snapcraft.yaml b/build-aux/snap/snapcraft.yaml
index e8e9e138..271561d0 100644
--- a/build-aux/snap/snapcraft.yaml
+++ b/build-aux/snap/snapcraft.yaml
@@ -67,6 +67,7 @@ parts:
     organize:
       snap/fractal/current/usr: usr
     build-packages:
+      - appstream
       - curl
       - libssl-dev
       - libgstreamer1.0-dev