should handle empty string crossOrigin

Expected behavior when empty string is given should be that of the
'anonymous' string.

Ref: https://developer.mozilla.org/en-US/docs/Web/HTML/CORS_settings_attributes

Author: chrisirhc

src/raven.js

@@ -760,7 +760,7 @@ function makeRequest(data) {
     var img = newImage(),
         src = globalServer + authQueryString + '&sentry_data=' + encodeURIComponent(JSON.stringify(data));
 
-    if (globalOptions.crossOrigin) {
+    if (globalOptions.crossOrigin || globalOptions.crossOrigin === '') {
         img.crossOrigin = globalOptions.crossOrigin;
     }
 

test/raven.test.js

@@ -1106,6 +1106,15 @@ describe('globals', function() {
             assert.equal(imageCache[0].crossOrigin, 'something');
         });
 
+        it('should populate crossOrigin if empty string', function() {
+            globalOptions = {
+                crossOrigin: ''
+            };
+            makeRequest({foo: 'bar'});
+            assert.equal(imageCache.length, 1);
+            assert.equal(imageCache[0].crossOrigin, '');
+        });
+
         it('should not populate crossOrigin if falsey', function() {
             globalOptions = {
                 crossOrigin: false