Set minimum railties version to match used methods

[kiskoza]

Hi. I tried to use committee-rails 0.6.1 with a Rails 5.0 application (in a CI pipeline) and it failed with an error message that lead me to writing this PR.

When I tried to figure out what the error message means, I checked the diff between 0.5.0 (which worked a month ago) and 0.6.1 and found that you're using a delegate_missing_to method in lib/committee/rails/request_object.rb, which was introduced in Rails 5.1.

I quickly checked out the repo, tried to run the test suite with Rails 5.0 and got this (similar what I'm seeing in the original CI)

An error occurred while loading ./spec/lib/methods_spec.rb.
Failure/Error: delegate_missing_to :@request

NoMethodError:
  undefined method `delegate_missing_to' for Committee::Rails::RequestObject:Class
  Did you mean?  DelegateClass
# ./lib/committee/rails/request_object.rb:5:in `<class:RequestObject>'
# ./lib/committee/rails/request_object.rb:4:in `<module:Rails>'
# ./lib/committee/rails/request_object.rb:3:in `<top (required)>'
# ./lib/committee/rails/test/methods.rb:2:in `require'
# ./lib/committee/rails/test/methods.rb:2:in `<top (required)>'
# ./lib/committee/rails.rb:2:in `require'
# ./lib/committee/rails.rb:2:in `<top (required)>'
# ./spec/spec_helper.rb:5:in `<top (required)>'

# ./spec/lib/methods_spec.rb:1:in `require'
# ./spec/lib/methods_spec.rb:1:in `<top (required)>'
# ------------------
# --- Caused by: ---
# LoadError:
#   cannot load such file -- committee-rails
#   ./spec/spec_helper.rb:5:in `<top (required)>'

As Rails 5.0 is not maintained anymore, I think the best is to drop the support here.

[kiskoza]

btw, I had issues running the tests with Rails 5.1 too, but I think it's just a missing config from the test application

[willnet]

I thought it would be more helpful to specify the version in actionpack and activesupport as well as in the railties.

[kiskoza]

I've updated the PR 👍

[willnet]

thanks a lot!