Use custom logger if configured, fallback to Rails.logger/STDOUT only if not

[dziemian007]

According to docs, you can set custom logger for APNs

APN.logger = Logger.new(File.join(Rails.root, 'log', 'apn_sender.log'))

But it's overwritten by Rails.logger (and it's cool beacause heroku deploys won't work otherwise, as discussed here #56). The drawback is that you cannot specify custom logger any more. So this patch should add usage of defined one, and fallback to Rails.logger/STDOUT if not.
What do you think?

[dziemian007]

Looks like travis build fails, maybe update used Ruby versions?

/home/travis/.rvm/gems/ruby-1.9.3-p547/gems/sidekiq-3.2.5/lib/sidekiq.rb:3:in `<top (required)>': Sidekiq 3.2.5 does not support Ruby 1.9. (RuntimeError)

[arthurnn]

not sure why this is better.