Bump config to ~>1.6.0

[carbonin]

This pulls in rubyconfig/config#167 which allows us to reference keys called "count" properly

[carbonin]

Before:

irb(main):005:0> Settings.workers.worker_base.defaults.count
=> 13

After:

irb(main):001:0> Settings.workers.worker_base.defaults.count
=> 1

[miq-bot]

Checked commit carbonin@471a887 with ruby 2.3.3, rubocop 0.47.1, haml-lint 0.20.0, and yamllint 1.10.0
1 file checked, 0 offenses detected
Everything looks fine. 👍

[bdunne]

👍 LGTM

[simaishi]

Gaprindashvili backport details:

$ git log -1
commit 0da70a94bd8db298dc80bae37b4a48a45b9213ba
Author: Brandon Dunne <brandondunne@hotmail.com>
Date:   Fri Jan 12 16:56:43 2018 -0500

    Merge pull request #16771 from carbonin/bump_config_gem_version
    
    Bump config to ~>1.6.0
    (cherry picked from commit c4095756b18517c211cbeb7fba66f8efcfffb1e6)