Improve `electron` support

[Szymon Marczak]

Currently the timings look this:

  timings: {
    start: 1576269343669,
    socket: undefined,
    lookup: undefined,
    connect: undefined,
    secureConnect: undefined,
    upload: 1576269343682,
    response: 1576269344083,
    end: undefined,
    error: undefined,
    phases: {
      wait: undefined,
      dns: undefined,
      tcp: undefined,
      tls: undefined,
      request: NaN,
      firstByte: 401,
      download: undefined,
      total: undefined
    }
  }

Missing:

• timings.end
• timings.phases.request
• timings.phases.download
• timings.phases.total

[Sindre Sorhus]

If you add any workarounds, ensure you also open Electron issues.