1. Install thin as web server instead of webrick. Write below line in gemfile and do bundle install.
2. In environments/development.rb file write below lines
config.force_ssl = true
config.ssl_port = 3001 # port will be your choice
3. Now start server using below command
thin start --ssl -p 3001
Now go to web browser and start your localhost:3000 with https://localhost:3000