Rackfile
```
#!/usr/bin/env rake

require 'rubygems'
require 'bundler'
require_relative ENV['CONFIG']

Bundler.require

namespace :db do
  desc 'Run migrations'
  task :migrate, [:version] do |_t, args|
    require 'sequel'    
    Sequel.extension :migration
    db = Sequel.connect(CONFIG[:database])

    if args[:version]
      puts "ver #{args[:version]}"
      Sequel::Migrator.run(db, 'db/migrations', target: args[:version].to_i)
    else
      puts 'ver latest'
      Sequel::Migrator.run(db, 'db/migrations')
    end
  end
end
```