Update Hello World to env: flex
Update Hello World to env: flex

GoogleCloudPlatform/getting-started-ruby,remi/getting-started-ruby,GoogleCloudPlatform/getting-started-ruby,GoogleCloudPlatform/getting-started-ruby,GoogleCloudPlatform/getting-started-ruby,remi/getting-started-ruby,remi/getting-started-ruby,remi/getting-started-ruby