Pass test_parse_big_integers on jruby

[okazu-dm]

Summary

I modified Generator.java and add INTEGER_HANDLER for passing test_parse_big_integers on jruby 9.2.0.0.
I think release of jruby 9.2.0.0 caused these failure. (I found this post http://jruby.org/2018/05/24/jruby-9-2-0-0)

Maybe this problem is mentioned in #336

note of implementation

The test failed because of Java::JavaLang::ClassCastException: org.jruby.RubyBignum cannot be cast to org.jruby.RubyFixnum.
I avoid this excpetion by adding INTEGER_HANDLER and use this handler instead of FIXNUM_HANDLER and BIGNUM_HANDLER.

[hsbt]

@headius Can you review this?

[kares]

this will only work on JRuby 9.2 (Ruby 2.5) compat but will break under 9.1 (Ruby 2.3).
... so whether this is okay depends on whether the release would target ruby >= 2.5

[kares]

setup an alternative fix, which works all the way back to JRuby 1.7 ... #361

[kares]

just to be clear, this piece did not raise any failures
but Fixnum/Bignum objects did take the generic path with the return GENERIC_HANDLER; on JRuby < 9.2 ... which isn't ideal/intended

[marcandre]

Commits should be squashed.

I can't set the reviewer to @headius (or maybe another JRuby user can review?)

[kares]

Hey Marc, this PR is defunct due #361 being merged ... there's special handling for the internal RubyFixnum/RubyBignum objects used by JRuby (these won't surface as a warning to use Integer).

[okazu-dm]

@kares Oh I found #361 fix this problem now. I close this PR.
Thanks for your kindness.