[shotwell] flatpak: Update exiv2 to include latest CVE fixes

[Jens Georg <jensgeorg src gnome org>]

commit 9be9879b93697868a8b8b120de96f74bc2ded97b
Author: Jens Georg <mail jensge org>
Date:   Sat Jun 9 02:53:58 2018 +0200

    flatpak: Update exiv2 to include latest CVE fixes

 flatpak/org.gnome.Shotwell.json | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)
---
diff --git a/flatpak/org.gnome.Shotwell.json b/flatpak/org.gnome.Shotwell.json
index 2cc7f78a..223fc187 100644
--- a/flatpak/org.gnome.Shotwell.json
+++ b/flatpak/org.gnome.Shotwell.json
@@ -99,8 +99,7 @@
                 {
                     "type": "git",
                     "url": "http://github.com/Exiv2/exiv2";,
-                    "branch": "0.26",
-                    "commit" : "2b5e6b7510f4c6f1c9efca08efc691292cf5c2c6"
+                    "commit" : "4aa57ad0217dfc509b42c5398602cede11fb8528"
                 }
             ]
         },