Allow crossDomain errors to be retried (ladjs#1194)

When using the retry() functionality on a bad connection, the browser can sometimes fail during a CORS OPTIONS request, which currently doesn't get retried. Superagent throws an error with crossDomain: true property in this case. We should retry instead, since the next attempt might succeed.

lib/should-retry.js

@@ -18,5 +18,6 @@ module.exports = function shouldRetry(err, res) {
   if (res && res.status && res.status >= 500) return true;
   // Superagent timeout
   if (err && 'timeout' in err && err.code == 'ECONNABORTED') return true;
+  if (err && 'crossDomain' in err) return true;
   return false;
-};
+};

test/client/xdomain.js

@@ -30,5 +30,21 @@ describe('xdomain', function(){
         next();
       });
     });
+
+    it('should handle x-domain failure after repeat attempts', function(next){
+      request
+      .get('//tunne127.com')
+      .retry(2)
+      .end(function(err, res){
+        try {
+          assert(err, 'error missing');
+          assert(err.crossDomain, 'not .crossDomain');
+          assert.equal(2, err.retries, 'expected an error with .retries');
+          next();
+        } catch(err) {
+          next(err);
+        }
+      });
+    });
   }
 });