Fix Appraisals and test against the intended version of Rails

[benpickles]

The pessimistic constraint was mis-targeted - for instance ~> 4.1 was actually specifying >= 4.1 && < 5.0 instead of the intended >= 4.1 && < 4.2 and thus the rails-4.1 Appraisal was actually testing against Rails 4.2.

I also dropped support for Rails 3.1 as it doesn't have watchable_files (

react-rails/lib/react/rails/railtie.rb

Line 20 in 46bb0b5

app.config.watchable_files.concat Dir["#{app.root}/app/assets/javascripts/**/*.jsx*"]

) and therefore needs some work. Also, I assume nobody's actually using react-rails with Rails 3.1 as there'd probably be a bug report by now.

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[benpickles]

Not sure why Travis is failing (undefined method api_only doesn't seem to mean anything in react-rails or rails itself), possibly just need to restart the job.

[rmosolgo]

Thanks for fixing this! I thought I knew how ~> worked but apparently not :P

LGTM once Travis is green

[rmosolgo]

Aaaand as you suspected, green after re-run!

Before

Only 2 Rails versions because minor versions were skipped:

After

[rmosolgo]

Thanks! 🎊