Print warning when used in development mode

[mperham]

I've had a number of issues where Sidekiq has stopped processing jobs in development mode. These all boiled down to people including rspec-sidekiq in the development group in their Gemfile. Could you please print a warning on bootup in the development environment since it is probably not what people want?

Bonus points: allow the user to disable the warning if they know they actually want to do this for some odd reason.

[philostler]

I've seen the odd case of this happening (obviously the warning in the README isn't enough). I'll print out a warning when jobs are going to be push to the testing array and not real Redis whatever the environment and I like the idea of the config option, I'll add that in as well.

I'd sorry if this has caused you problems with issues being raised. I'll push this out in 1.0.0 very soon

[philostler]

P.s. I've also seen some people getting confused thinking that it's rspec-sidekiq providing the testing array support. That's certainly not my intention and I'll make it clearer in the README that it's sidekiq providing this feature and not rspec-sidekiq.