Fixed error on requiring 'classifier-reborn' without using Redis

[valeronm]

I have tried to use the gem without using redis and got this error

Bundler::GemRequireError: There was an error while trying to load the gem 'classifier-reborn'.
Gem Load Error is: uninitialized constant NoRedisError
Backtrace for gem load error is:
/mnt/d/documents/projects/classifier-reborn/lib/classifier-reborn/backends/bayes_redis_backend.rb:4:in `rescue in <top (required)>'
/mnt/d/documents/projects/classifier-reborn/lib/classifier-reborn/backends/bayes_redis_backend.rb:1:in `<top (required)>'
/mnt/d/documents/projects/classifier-reborn/lib/classifier-reborn/bayes.rb:9:in `require_relative'
/mnt/d/documents/projects/classifier-reborn/lib/classifier-reborn/bayes.rb:9:in `<top (required)>'
/mnt/d/documents/projects/classifier-reborn/lib/classifier-reborn.rb:29:in `require_relative'
/mnt/d/documents/projects/classifier-reborn/lib/classifier-reborn.rb:29:in `<top (required)>'

I think that we need to manually require classifier-reborn/backends/bayes_redis_backend before using redis backend.