use ruby 2.1.2 on travis

we'll be upgrading ruby to 2.1.2
upgrade to ruby 2.1.2

- upgrade `capybara` and `sass-rails`
Remove gemfury source from Gemfile as it's redundant
previous version of govuk_frontend_toolkit was yanked update to latest

Changes did not affect the trade-tariff-frontend
Update README
update capybara, poltergeist, phantomjs
Fix asset compilation issue in test by including the group

Also fixes rel external style after updates to govuk_frontend_toolkit
Use production slimmer asset host
Update gds-api-adapters
Fix colspan on no measures message
Cache bundled gems
clean up travis file
Merge pull request #140 from bitzesty/ruby-2.1.2

use ruby 2.1.2
[76519868] show last successful sync date

Stub `TariffUpdate.all` on specs so we don't have to use a cassette for each request

[PT](https://www.pivotaltracker.com/story/show/76519868)
Update need id to new format

Using 100233: Find out the correct trade tariffs for items I am
importing or exporting.

Seems like the closest match as B659 is not longer there
Merge pull request #144 from alphagov/fix-need-id

Update need id to new format
Merge pull request #141 from bitzesty/76519868-show-last-updated

[76519868] show last successful sync date
upgrade to rails 4

also some amendments to specs to make them work
force #to_s when parameterizing Section
use `xvfb` to run tests on travis