update description about rb_cFixnum and rb_cBignum.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@55465 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
update description about rb_cFixnum and rb_cBignum.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@55465 b2dd03c8-39d4-4d8f-98ff-823fe69b080e