[gnome-books/wip/carlosg/tracker3] flatpak: Add libgsf dependency

[Carlos Garnacho <carlosg src gnome org>]

commit d875d79c40cdffa1167fe77536848064eed6f017
Author: Carlos Garnacho <carlosg gnome org>
Date:   Tue Feb 16 13:16:52 2021 +0100

    flatpak: Add libgsf dependency
    
    This is needed by tracker-miners for epub documents.

 flatpak/org.gnome.Books.json | 12 ++++++++++++
 1 file changed, 12 insertions(+)
---
diff --git a/flatpak/org.gnome.Books.json b/flatpak/org.gnome.Books.json
index a80bab77..aefbba7a 100644
--- a/flatpak/org.gnome.Books.json
+++ b/flatpak/org.gnome.Books.json
@@ -104,6 +104,18 @@
                 }
             ]
         },
+        {
+            "name" : "libgsf",
+            "cleanup" : [
+                "/bin"
+            ],
+            "sources": [
+                {
+                    "type": "git",
+                    "url": "https://gitlab.gnome.org/GNOME/libgsf.git";
+                }
+            ]
+        },
         {
             "name": "evince",
             "buildsystem": "meson",