[geary] Fix Flatpak build.

[Michael Gratton <mjog src gnome org>]

commit 9a89d7e0379776f520ac8d08d693601019ef39c9
Author: Michael James Gratton <mike vee net>
Date:   Sat Dec 2 22:10:36 2017 +1100

    Fix Flatpak build.
    
    * org.gnome.Geary.json: Add libunwind dep, point libgee back to master
      while we're here.

 org.gnome.Geary.json |   12 +++++++++++-
 1 files changed, 11 insertions(+), 1 deletions(-)
---
diff --git a/org.gnome.Geary.json b/org.gnome.Geary.json
index 65076f8..d1de0a4 100644
--- a/org.gnome.Geary.json
+++ b/org.gnome.Geary.json
@@ -84,7 +84,7 @@
                 {
                     "type": "git",
                     "url": "https://git.gnome.org/browse/libgee";,
-                    "tag": "0.20.0"
+                    "branch": "master"
                 }
             ]
         },
@@ -99,6 +99,16 @@
             ]
         },
         {
+            "name": "libunwind",
+            "sources": [
+                {
+                    "type": "git",
+                    "url": "https://git.savannah.gnu.org/git/libunwind.git";,
+                    "branch": "master"
+                }
+            ]
+        },
+        {
             "name": "geary",
             "sources": [
                 {