jsHint error fix.

Source/Core/BingMapsApi.js

@@ -29,7 +29,7 @@ define([
     BingMapsApi.defaultKey = undefined;
 
     var printedBingWarning = false;
-    var errorCredit = undefined;
+    var errorCredit;
     var errorString = 'This application is using Cesium\'s default Bing Maps key.  Please create a new key for the application as soon as possible and prior to deployment by visiting https://www.bingmapsportal.com/, and provide your key to Cesium by setting the Cesium.BingMapsApi.defaultKey property before constructing the CesiumWidget or any other object that uses the Bing Maps API.';
 
     BingMapsApi.getKey = function(providedKey) {