Remove spurious warning from snap metadata

I don't know why this chmod didn't work previously
...it was a long time ago when I wrote this

.gitignore

@@ -0,0 +1 @@
+*.snap

snap/hooks/install

@@ -3,6 +3,4 @@
 set -e
 
 cp $SNAP/default.conf $SNAP_DATA/config
-# The config file should not be world readable, but the snap user can't read it
-# either if it is chmodded. How to solve this?
-#chmod 600 $SNAP_DATA/config
+chmod 600 $SNAP_DATA/config

snap/snapcraft.yaml

@@ -1,5 +1,6 @@
 name: mythicbeastsddns
 version: 'git'
+base: core22
 summary: Automatically update dynamic dns for your Mythic Beasts hosts
 description: |
   Mythic Beasts customers can use this snap to automatically update dynamic dns
@@ -7,12 +8,11 @@ description: |
   ipv4hostname and ipv6hostname using the `snap set` command as detailed at 
   https://docs.snapcraft.io/reference/snap-command#set . Activate the updater by
   setting the updateipv4 and/or updateipv6 keys to "yes".
-  .
-  BEWARE - passwords are stored in world-readable plain text. Until I can find a
-  way around this problem do not use this snap in production.
 grade: stable
 confinement: strict
-architectures: [ all ]
+architectures:
+  - build-on: [amd64]
+    build-for: [all]
 
 apps:
   mythicbeastsddns: