If I don't want to specify any encoding including gzip,
then I can set `options.encoding` to `null`.
Here's quote from **request**:
`encoding` - Encoding to be used on `setEncoding` of response data. If set to `null`, the body is returned as a Buffer.
Merge pull request #47 from trantorLiu/master

Let `options.encoding = null` be really null (it should not accept `gzip`)