Add `(require 'cl)` for cdddr, caddr

In enh-ruby-mode.el, cdddr and caddr are used.
They are not defined by default.

Because in most cases other libraries require `cl`,
which defines them, this problem doesn't come out.
Merge pull request #25 from vzvu3k6k/fix/missing-defs-of-cdddr-caddr

caddr and cdddr are not defined by default