Updating of Ruby based packages from now.

[Takahiro Kambe <taca%NetBSD.org@localhost>]

Hi,

I start updating of Ruby based packages from now.

* Reduce support for Ruby 1.8.7.
* Change of PKGBASE for Ruby 2.1.5: "ruby215-" to "ruby21-" and
  version in include/library directories (2.1.5 => 2.1.0).
* Change value of @os instance variable of Gem::Platform.  It cause
  change of GEM_EXTSDIR.
* Importing Ruby 2.2.1.

In these commit work, Ruby packages would be inconsitent state.

Best regards.

-- 
Takahiro Kambe <taca%NetBSD.org@localhost>/<taca%back-street.net@localhost>