Fix .defaults({opt: value}) erasing base options
Fix .defaults({opt: value}) erasing base options

Using `require('request-promise').defaults({timeout: 2000})` - or any other value - will erase base values used by `require-promise` (simple & resolveWithFullResponse flag for the moment).

This pull request fixes that.
Jonekee/request-promise,midgethoen/request-promise,martinsson/request-promise,request/request-promise