Test fail with non-tty environment

[hsbt]

@aycabta

Ruby CI detects a broken code with rdoc-6.0.0.beta2.

https://rubyci.org/logs/rubyci.s3.amazonaws.com/ubuntu1604/ruby-trunk/log/20170912T093009Z.fail.html.gz

IO.console is not provided non-tty environment like cron job. I reverted 8cfa11d

Maybe, We should skip related tests with JRuby.

[aycabta]

I understand what you explained, thank you for fixing bug what I made by #518.