src/ScraperPromise.js
function(callback) {
		this.promises.push(function then(done, utils) {
			done(null, callback(utils.lastReturn, utils));
		});
		return this;
	}
function(callback) {
		this.promises.push(function then(done, utils) {
			done(null, callback(utils.lastReturn, utils));
		});
		return this;
	}
function ( callback ) { this . promises . push ( function then ( done , utils ) { done ( null , callback ( utils . lastReturn , utils ) ) ; } ) ; return this ; }
Sets a generic promise.

@param  {!function()} callback Callback.
@return {!ScraperPromise} This object, so that new promises can
be made.
@public
Sets a generic promise .