Log Message:
Update ruby2ruby to 2.4.0.

=== 2.4.0 / 2017-07-17

* 1 major enhancement:

  * Major overhaul. Process methods no longer mutate arguments.

* 1 minor enhancement:

  * Now SEXP_STRICT=1 clean.

* 2 bug fixes:

  * Fixed 2.4 Fixnum deprecation warning
  * Fixed for new 24 parser.