Update eslint

[froatsnook]

@simov I saw you mention updating eslint and decided to have a go at it.

In general I tried to avoid rocking the boat. There are some new options which raise some issues since the code style was not consistent. I just disabled these options in .eslintrc for now.

no-shadow
Sounds like a good idea to me. There are 21 no-shadow issues in the code right now.

key-spacing
At the moment the codebase uses a mixes of the two styles, which means eslint can't help us.

no-multi-spaces
There are a lot of inconsistencies in the code with this one:

// test-baseUrl.js
var http = require('http')
  , request = require('../index')
  , tape = require('tape')
  , url = require('url')

vs

// test-agentOptions.js
var request = require('../index')
  , http    = require('http')
  , server  = require('./server')
  , tape    = require('tape')

as well as:

// lib/getProxyFromURI.js:67
    return process.env.HTTPS_PROXY ||
           process.env.https_proxy ||
           process.env.HTTP_PROXY  ||
           process.env.http_proxy  || null

[simov]

Thanks, @froatsnook that might come in handy. I like that approach of introducing it with minimum changes to the code. Also only 3 additional disabled options is not that bad I think. What I wanted to add was "indent": [2, 2] for the 2 space indentation, because it is disabled by default.

[froatsnook]

@simov Good call. That found a few indentation errors.

[FredKSchott]

+10000 So glad we can finally update out of node v0.8 purgatory

[simov]

This PR is looking good to me, we can think about enabling some of the eslint options later. The only thing that I'll suggest is to rebase all commits into one, as they are too small to have any meaning on its own.

[froatsnook]

@simov OK, done!

[simov]

Thanks @froatsnook 👍