fix: update rb_cData to rb_cObject to support Ruby 3.2+

[flavorjones]

rb_cData was deprecated in Ruby 3.1 and removed in Ruby 3.2.

• https://github.com/ruby/ruby/commit/089b7a8
• https://bugs.ruby-lang.org/issues/3072#note-15

Fixes #3

Without this change, compiling results in this error:

compiling ../../../../ext/cppjieba_rb/internal.cc
../../../../ext/cppjieba_rb/internal.cc: In function ‘void Init_internal()’:
../../../../ext/cppjieba_rb/internal.cc:166:81: error: ‘rb_cData’ was not declared in this scope; did you mean ‘rb_eFatal’?
  166 |     rb_cCppjiebaRb_Internal = rb_define_class_under(rb_mCppjiebaRb, "Internal", rb_cData);
      |                                                                                 ^~~~~~~~
      |                                                                                 rb_eFatal
make: *** [Makefile:214: internal.o] Error 1

[erickguan]

Thanks for the details!