Fix node.js handling of multi-byte UTF8 characters (#6761)

* Fix node.js handling of multi-byte UTF8 characters

Fixes issue #6280, where the node.js API doesn't properly handle
multi-byte UTF8 characters received from the driver.

* Specify encoding in toString

javascript/node/selenium-webdriver/http/index.js

@@ -235,7 +235,7 @@ function sendRequest(options, onOk, onError, opt_data, opt_proxy, opt_retries) {
       var resp = new httpLib.Response(
           /** @type {number} */(response.statusCode),
           /** @type {!Object<string>} */(response.headers),
-          body.join('').replace(/\0/g, ''));
+          Buffer.concat(body).toString('utf8').replace(/\0/g, ''));
       onOk(resp);
     });
   });