sqlite3 gem also required for production, not only for development

otherwise, the following commands

    bundle install --without development test
    bundle exec rake fulcrum:setup db:setup

fail with

```
rake:23:in `<main>'
Couldn't create database for {"adapter"=>"sqlite3", "database"=>"db/test.sqlite3", "pool"=>5, "timeout"=>5000}
rake aborted!
Please install the sqlite3 adapter: `gem install activerecord-sqlite3-adapter` (sqlite3 is not part of the bundle. Add it to Gemfile.)
```