Specify test_order to not show deprecation message

Running the following test was showing the below deprecation message;
the deprecation message is shown even when the entire suite is run with 
`rake test`:
> cd raities
> ruby -w -Itest test/generators/generator_test.rb

    DEPRECATION WARNING: You did not specify a value for the
    configuration option `active_support.test_order`. In
    Rails 5, the default value...