RapidConnect: misc fixes (html escaping, typo, dependency)

Hi Bradley,

I'm doing the finishing touches on the Tuakiri Rapid Connect and I have a few things I'd like to contribute back - just minor fixes:
* Gemfile: update ffi dependency to 1.9.5 (1.9.4 has disappeared and bundler could not get it)
* DevelopersDoc: rendered MD: prevent html_escaping (the developer doc was getting HTML-escaped since erubis was pulled in)
* Views: fix typo in registration/complete.erb (there was an incomplete sentence of the TEST confirmation page)

Hope these are easy to merge.

Cheers,
Vlad