Set up instructions: remove Nitrous or replace with alternative

[SteveBarnett]

Helloes. 👋 😺

In the ruby section of the setup tutorial we suggest using a Nitrous. Unfortunately, it shut down on November 14th, 2016.

Cloud9 seems to be a popular alternative and has a free tier. Should we update the instructions to suggest C9 (or some other cloud IDE) instead of Nitrous?

[SteveBarnett]

Ooh, I see we already suggest in on http://tutorials.codebar.io/ for the PHP course. :)

[matyikriszta]

@SteveBarnett I have updated every mention of nitrous to cloud9, as per #351. Going to close this issue.