Try fixing Travis builds.
Try fixing Travis builds.

- Nokogiri can no longer be installed on Ruby 2.0. Disabling testing on
Ruby 2.0.
- Travis is failing to install Ruby 2.3. Trying if specifying patch
level will fix it.

Otherwise tests are passing locally. Not sure what's causing them
to fail on Travis.

Signed-off-by: Anurag Priyam <6e6ab5ea9cb59fe7c35d2a1fc74443577eb60635@gmail.com>

yeban/sequenceserver,elsiklab/sequenceserver,yeban/sequenceserver,elsiklab/sequenceserver,yeban/sequenceserver,elsiklab/sequenceserver,yeban/sequenceserver