move ECONNRESET log from error to debug

[ziimakc]

I'm new to js, github and this is my first PR, so feel fre to change anything.
Closes #1361

Problem
Google chrome browser keep-alive socket connection to server, so after 2 min of any https request, or if client will close browser window - server socket will timeout.

After that error will be logged:

ERROR [2019-01-03 12:24:09.858 +0000] (11508 on PredatorRTW):
    msg: "client error"
    err: {
      "type": "Error",
      "message": "socket hang up",
      "stack":
          Error: socket hang up
              at TLSSocket.onSocketClose (_tls_wrap.js:737:23)
              at TLSSocket.emit (events.js:187:15)
              at _handle.close (net.js:616:12)
              at Socket.done (_tls_wrap.js:384:7)
              at Object.onceWrapper (events.js:273:13)
              at Socket.emit (events.js:182:13)
              at TCP._handle.close (net.js:616:12)
      "code": "ECONNRESET"
    }

Proposal
Errors should be something important and this one should be moved in less important category. As @mcollina suggested in previos conversation - into debug.

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 Code of conduct

[ziimakc]

Can't run tests for some reason. But for this change i don't think it's needed.

[cemremengu]

@RTVV tests are not being run since linting is failing. You will need to fix these.

  829:5   error  Expected space(s) after "if"         keyword-spacing
  829:17  error  Expected '===' and instead saw '=='  eqeqeq

[mcollina]

I think it should just be debug  for everything.

[ziimakc]

Ok, i've moved client error to debug. What is the next step?

[mcollina]

LGTM

I think we can just land this.

[cemremengu]

@mcollina port to 1.x ?

[delvedor]

LGTM

[mcollina]

@cemremengu yes please!

[github-actions]

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