Update rubies in CI
Update rubies in CI

- Ruby 2.0.0 and 1.9.3 have reached their EOL, so ignore failure from
  now on.

- Update JRuby 1.7 to 1.7.26 and remove it from `allow_failures`

- Update JRuby 9000 to 9.1.5.0

- Retire rbx

- Use `gem install --conservative` instead of checking with `gem query`

sparklemotion/mechanize,sparklemotion/mechanize,flavorjones/mechanize,eligoenergy/mechanize,eligoenergy/mechanize