Fix dummy app database.yml for ENV[DB] = sqlite3

This is the same fix as #5613, but this time for the dummy app
`database.yml` template rather than for the install generator.

I've now also tested this locally, and it seems to work.

(cherry picked from commit 0a8c2b8)

core/lib/generators/spree/dummy/templates/rails/database.yml

@@ -3,7 +3,7 @@
  'mysql'
  when 'postgres', 'postgresql'
  'postgres'
- when 'sqlite', '', nil
+ when /sqlite3?/, '', nil
  'sqlite'
  else
  raise "Invalid DB specified: #{ENV['DB']}"