paranoia >= 2.5.1 assumes Rails constant is defined

[lionelchauvin]

3572129#diff-a7b13874ca65cce80cfa49aa594d2cbb4a486019b334c831ce0bd5de605f2533R1

This commit checks if Rails.env.test? in order to add rspec matchers but rails is not a dependency of paranoia.
Gems that are only dependent on activerecord (and paranoia) crash on this line.

[lionelchauvin]

It could be replaced by:
if !(defined? Rails) || Rails.env.test?

or
if ENV['RAILS_ENV'] == 'test'

or don't require 'paranoia/rspec' and let developpers do it.

[mathieujobin]

this is merged in core but still not tagged release
#529