Revert changes introduced in https://github.com/request/request/pull/1282

Reverting back the change introduced in https://github.com/request/request/pull/1282

For some reason this change brakes the form option when it's object.

From the docs

> form - when passed an object or a querystring, this sets body to a querystring representation of value, and adds Content-type: application/x-www-form-urlencoded header.

No idea why it brakes yet, that's just the fix. I can confirm the bug by running my tests in https://github.com/simov/purest