[nautilus] Flatpak: Use Sdk 3.28

[Carlos Soriano <csoriano src gnome org>]

commit a4e797d9746887e97eb97262482933e49e7630c7
Author: Carlos Soriano <csoriano1618 gmail com>
Date:   Fri Mar 16 15:00:34 2018 +0000

    Flatpak: Use Sdk 3.28

 build-aux/flatpak/org.gnome.Nautilus.json | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/build-aux/flatpak/org.gnome.Nautilus.json b/build-aux/flatpak/org.gnome.Nautilus.json
index df0260e03..d0051f072 100644
--- a/build-aux/flatpak/org.gnome.Nautilus.json
+++ b/build-aux/flatpak/org.gnome.Nautilus.json
@@ -1,7 +1,7 @@
 {
     "app-id": "org.gnome.Nautilus",
     "runtime": "org.gnome.Platform",
-    "runtime-version": "master",
+    "runtime-version": "3.28",
     "sdk": "org.gnome.Sdk",
     "command": "nautilus",
     "tags": ["devel", "development", "nightly"],