mix: clean dependencies for great good

[dch]

It seems we can simplify mix dependencies dramatically now - I believe the lager and mochiweb issues of last year are all gone. Incidentally this also resolves a pathological mix deps.update --all on our app which consumes over 50GiB of RAM while doing the dependency resolution, so ... that's a bonus.

I'm not really able to do significant testing of all the related Elixir & OTP versions, but "works for me" on OTP 22.1.5, RabbitMQ 3.8.1, and Elixir 1.9.3

[dch]

^ fails only with Elixir 1.6, which AFAICT isn't supported. I think it's reasonable to forge on & commit this.

[whatyouhide]

👏

[ono]

I'd like to support 3.7.x on 1.x if possible. Let me think bit more about the best way supporting 3.8.x.

[ono]

Sorry for being late. I am going to merge this and release this as 1.4.0-rc.0.

• We remove some compatibilities with lower version of amqp_client and Elixir
• It has some impact so patch level version bump is not sufficient
• I believe we can do it with a minor version bump as it doesn't contain any API changes
• I will also update travis config and wiki page

Thanks!