Use Ruby 2.2.0 preview 1

- Updated kgio gem to latest version.
- Earlier version has problems in installation on Ruby 2.2.0-preview1
Bump to raindrops is also required for Ruby 2.2.0

- Reference: http://raindrops.bogomips.org/ChangeLog.html
Merge pull request #270 from codetriage/ruby22

Use Ruby 2.2.0 preview 1