Migrate all spree pref. keys to the new format

We realized in Spree v2.1 they follow this format instead and this is
what's causing issues to Katuma production.

This will remove the duplicate ones and convert the current preferences
to the new thus, keeping the values.

db/migrate/20200623140437_fix_preferences_keys.rb

@@ -0,0 +1,11 @@
+class FixPreferencesKeys < ActiveRecord::Migration
+  def up
+    new_preferences = Spree::Preference.where("key like '/%'")
+    new_preferences.delete_all
+
+    Spree::Preference.update_all("key = '/' || key")
+  end
+
+  def down
+  end
+end

db/schema.rb

@@ -11,7 +11,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 20200508101630) do
+ActiveRecord::Schema.define(version: 20200623140437) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"