feat(resources): export DNS records

Support exporting DNS records in BIND format.

Signed-off-by: Terin Stock <terin@cloudflare.com>

Author: mikehardenize

lib/resources/DNSRecords.js

@@ -44,6 +44,22 @@ module.exports = auto(
       path: ':id',
     }),
 
+    /**
+     * export retrieves all of a zone's DNS Records in BIND configuration format.
+     *
+     * @function export
+     * @memberof DNSRecords
+     * @instance
+     * @async
+     * @param {string} zone_id - The zone ID
+     * @returns {Promise<Object>} The DNS browser response object.
+     */
+    export: method({
+      method: 'GET',
+      path: 'export',
+      json: false,
+    }),
+
     /**
      * browse allows for listing all DNS Records for a zone
      *