set db environment to development

ENV['RACK_ENV'] = 'development'

This line of code sets the environment variable RACK_ENV to the string 'development'. In Ruby applications, the environment variable RACK_ENV is often used to specify the environment in which the application is running. Setting it to 'development' indicates that the application should run in the development environment. This typically means that the application will use a development database and configuration settings suited for development purposes, such as debugging and testing.