[gnome-mines] snap: Update for core18

[Ken VanDine <kvandine src gnome org>]

commit b8477d7c98baccd6e90f75f0aa345f16b9bd88e4
Author: Ken VanDine <ken vandine canonical com>
Date:   Thu Mar 7 22:34:35 2019 -0500

    snap: Update for core18

 snap/snapcraft.yaml | 19 +++++++++++++++----
 1 file changed, 15 insertions(+), 4 deletions(-)
---
diff --git a/snap/snapcraft.yaml b/snap/snapcraft.yaml
index 04d39a7..6eba089 100644
--- a/snap/snapcraft.yaml
+++ b/snap/snapcraft.yaml
@@ -13,6 +13,7 @@ description: |
 
 grade: stable # must be 'stable' to release into candidate/stable channels
 confinement: strict
+base: core18
 
 # Launchpad doesn't recognize these fields yet
 passthrough:
@@ -20,10 +21,10 @@ passthrough:
   title: GNOME Mines
 
 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
@@ -54,8 +55,18 @@ apps:
       GSETTINGS_SCHEMA_DIR: $SNAP/share/glib-2.0/schemas
 
 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-mines:
-    build-attributes: [no-system-libraries]
     after: [desktop-gnome-platform]
     source: .
     source-type: git
@@ -81,7 +92,7 @@ parts:
   libraries:
     plugin: nil
     stage-packages:
-      - libgnome-games-support-1-2
+      - libgnome-games-support-1-3
       - libgee-0.8-2
     prime:
       - "usr/lib/*/libgnome-games-support-1.so.*"