Allow custom HTTP status code error ranges (#308)

Adding support for custom HTTP status code error ranges

lib/helpers/settle.js

@@ -0,0 +1,18 @@
+'use strict';
+
+/**
+ * Resolve or reject a Promise based on response status.
+ *
+ * @param {Function} resolve A function that resolves the promise.
+ * @param {Function} reject A function that rejects the promise.
+ * @param {object} response The response.
+ */
+module.exports = function settle(resolve, reject, response) {
+  var validateStatus = response.config.validateStatus;
+  // Note: status is not exposed by XDomainRequest
+  if (!response.status || !validateStatus || validateStatus(response.status)) {
+    resolve(response);
+  } else {
+    reject(response);
+  }
+};