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
Revert "use `xvfb` to run tests on travis"

This reverts commit 435406dd20506677c77c6897a4684d66e8134944.
Merge pull request #145 from bitzesty/rails-4

upgrade to rails 4