Upgraded to the latest conformance suite
Do not update conformance tests in test:conformance rake task.
Update rubygems on Travis CI to fix build failure on Ruby 1.8.7.

Can be reverted once new Ruby VMs are deployed to Travis CI (see
https://github.com/travis-ci/travis-ci/issues/1793#issuecomment-31369335
for more information).
Do not downcase usernames during linkification.
Fix link_to_screen_name RSpec matcher.