fix: add closeClient on namespaced client

[gkampitakis]

Solves

As discussed on the issue #75 there is no closeClient when providing a Redis client in a namespace.

I just have a question regarding this solution, if I pass

{
  host: '127.0.0.1',
  closeClient: true
}

does this mean I am adding two onClose hooks ?

Checklist

• run npm run test and npm run benchmark
• tests and/or benchmarks are included
• documentation is changed or added
• commit message and code follows the Developer's Certification of Origin
  and the Code of conduct

[mcollina]

lgtm