header type check bug

[Zaynex]

In electron@5.x
I find an interesting bug.

I set headers with object, but the object type gave Map, so the header think it's not an object

      header: function (field, value) {
        if (is(field).a(Object)) {
          for (var key in field) {
            if (Object.prototype.hasOwnProperty.call(field, key)) {
              $this.header(key, field[key])
            }
          }

          return $this
        }

        var existingHeaderName = $this.hasHeader(field)
        $this.options.headers[existingHeaderName || field] = value

        return $this
      },

see the error stack:

name.toLowerCase is not a function
    at Object.hasHeader (/Users/xiwz/ynote/electron-sdk/example/node_modules/unirest/index.js:93:21)
    at Object.header (/Users/xiwz/ynote/electron-sdk/example/node_modules/unirest/index.js:198:40)

But actually I send the object

{
  'Content-Type': '',
  'Cookie': ''
}

I think this bug belongs to electron.It changed the Object default behavior. But unirest type check is unsafe.

I wonder if you would like to improve it ? I am willing to send a PR.

My solution:

if (check.prototype) check = Object.prototype.toString.call(check.prototype).slice(8, -1).toLowerCase()