code: function(zip, callback) {
  
  			var queryString = "?postalCode="+zip;
  			httpGet(queryString, function(err, results) {
  				callback(err, results);
  			});
  
  		}
docs: callback for getForecastByZipCode
  @callback module:asthma-forecast/client~getForecastByZipCodeCallback
  @param {Object} [err] error calling Propeller API
  @param {Object} [result] forecast
   
  getForecastByZipCode
  @param {String} options.zipCode Zip code
  @param {module:asthma-forecast/client~getForecastByZipCodeCallback} [callback] callback