<b> replaced by <strong>
Change version of Rubinius

I hope this change will make Travis-ci stop failing…
Stop testing on Rubinius

Honesty, I love Rubinius but I just can't continue to have all build failed
because of stupid “Can't found xxx lib” errors.
Merge branch 'strong_instead_of_b' of https://github.com/rudyrigot/ruby-kit