numeric.c: prefer rb_check_arity
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@54474 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
numeric.c: prefer rb_check_arity
instead of rb_scan_args for a simple optional argument.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@54474 b2dd03c8-39d4-4d8f-98ff-823fe69b080e