Support/require ActiveRecord 4.0.0.beta1

Two files needed changes to make the specs pass.

* lib/standalone_migrations.rb:

	`rake db:create` was ignoring ENV['DB']. It seems like ActiveRecord now loads the DB configuration from `ENV['RAILS_ENV']` when it is required, which it did not do before. Setting `ENV['RAILS_ENV']` before requiring ActiveRecord ensures it has the intended environment.

* spec/standalone_migrations_spec.rb:

	Newly created migrations now use `change()` instead of `up()` and `down()`. Updated specs to expect/use the new behavior.
Version bump to 2.0.6