Add basic Travis CI configuration
[gem] Lock nokogiri to the last version that supports 1.8.7
Use the bridgepdx theme in CI, as the default is borked
Switch Gemfile source to https://rubygems.org
Downgrade rubygems to 1.8.25 before Travis CI runs
Run migrations before testing in CI
Don't require secrets in the test environment
Run tests in UTC, instead of the local time zone