a couple of changes needed for local install

[kaymo4]

I hope this is useful for others, I have made 2 changes

1. gemfile: Unknown ruby interpreter version (do not know how to handle): >=2.2,<3.0.
   changed this: ruby '>= 2.2', '< 3.0'
   with this: ruby '2.5.1'

2. config/application.rb: rake fails
   #Bundler.require(*Rails.groups) fails
   Bundler.require
   #add this otherwise rake fails
   require 'rack/cors'

Thanks again for a great app!