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']}"