add regression testing specs

[ajb]

cf #113.

• this test will fail if there's significant visual difference between the old and new behavior of a test
• to create a new regression spec, we would create an isolated view (a la /spec/dummy/app/views/home/regression/dropdown.rb), and add a test to spec/regression_spec.rb)

See https://github.com/ronen/rspec-page-regression for more.

I think this is handy to have, especially for interactive bits. I would consider adding regression specs for:

• Dropdowns (all variations)
• Selects
• Dropdown selects
• Modals
• Checkbox/radio (since styling these is so tricky)

[ajb]

@jrubenoff: curious to hear your thoughts on this.

[jrubenoff]

Seems :+1: to try out, at least.

[jrubenoff]

Just realized Github doesn't allow comments on images, so, one qualifier: assuming expected.png is automatically generated, it doesn't appear to be loading Typekit fonts.

Something to keep in mind if tests are generating screenshots that look "broken", even when the style guide is fine.

[ajb]

Yeah, so the dummy app runs on the example.com host, which we need to whitelist for Typekit.

Also, I've gotta figure out why the specs are failing before this can get merged.