[gexiv2] ci: Force use of exiv2 0.27 branch, not tag

[Jens Georg <jensgeorg src gnome org>]

commit 7874af4274b4a729db5d76a22a1a4b3fa45e168d
Author: Jens Georg <mail jensge org>
Date:   Fri Jan 18 16:59:15 2019 +0100

    ci: Force use of exiv2 0.27 branch, not tag

 build-aux/org.gnome.GExiv2-stable.json | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/build-aux/org.gnome.GExiv2-stable.json b/build-aux/org.gnome.GExiv2-stable.json
index 2bccdb3..0c442aa 100644
--- a/build-aux/org.gnome.GExiv2-stable.json
+++ b/build-aux/org.gnome.GExiv2-stable.json
@@ -35,7 +35,7 @@
                 {
                     "type" : "git",
                     "url" : "https://github.com/Exiv2/exiv2/";,
-                    "branch" : "0.27"
+                    "branch" : "refs/heads/0.27"
                 }
             ]
         },