[gnome-mahjongg/gnome-3-22] snap: Updated for core18

[Ken VanDine <kvandine src gnome org>]

commit 13ae19e7058d7098784bd76e5d5290ae5c08027e
Author: Ken VanDine <ken vandine canonical com>
Date:   Thu Mar 7 21:32:44 2019 -0500

    snap: Updated for core18

 snap/snapcraft.yaml | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)
---
diff --git a/snap/snapcraft.yaml b/snap/snapcraft.yaml
index 775658b..c29f395 100644
--- a/snap/snapcraft.yaml
+++ b/snap/snapcraft.yaml
@@ -15,12 +15,13 @@ description: |
 
 grade: stable # must be 'stable' to release into candidate/stable channels
 confinement: strict
+base: core18
 
 plugs:
-  gnome-3-26-1604:
+  gnome-3-28-1804:
     interface: content
     target: $SNAP/gnome-platform
-    default-provider: gnome-3-26-1604
+    default-provider: gnome-3-28-1804
   gtk-3-themes:
     interface: content
     target: $SNAP/data-dir/themes
@@ -51,8 +52,18 @@ apps:
       PATH: $SNAP/usr/games:$PATH
 
 parts:
+  desktop-gnome-platform:
+    source: https://github.com/ubuntu/snapcraft-desktop-helpers.git
+    source-subdir: gtk
+    plugin: make
+    make-parameters: ["FLAVOR=gtk3"]
+    build-packages:
+      - build-essential
+      - libgtk-3-dev
+    override-build: |
+      snapcraftctl build
+      mkdir -pv $SNAPCRAFT_PART_INSTALL/gnome-platform
   gnome-mahjongg:
-    build-attributes: [no-system-libraries]
     after: [desktop-gnome-platform]
     source: .
     source-type: git