Typings for stringifyUrl don't allow empty query

[IlyaSemenov]

This is a valid code:

> require('query-string').stringifyUrl({url:'/some'})
'/some'

Yet it emits a TS error:

Argument of type '{ url: string; }' is not assignable to parameter of type 'UrlObject'.
  Property 'query' is missing in type '{ url: string; }' but required in type 'UrlObject'.ts(2345)

I believe query must be marked as query? here:

query-string/index.d.ts

Lines 369 to 375 in 2a17881

	export interface UrlObject {
	readonly url: string;
	/**
	Overrides queries in the `url` property.
	*/
	readonly query: StringifiableRecord;