Update Zend Feed to latest stable

Updated composer.json to require 2.3.* and ran composer update zendframework/zend-feed zendframework/zend-stdlib zendframework/zend-escaper

+++ b/core/vendor/zendframework/zend-feed/Zend/Feed/Reader/Reader.php
@@ -299,6 +298,11 @@ public static function importRemoteFeed($uri, Http\ClientInterface $client)
     public static function importString($string)
     {
+        $trimmed = trim($string);
+        if (!is_string($string) || empty($trimmed)) {
+            throw new Exception\InvalidArgumentException('Only non empty strings are allowed as input');
+        }

This change seems to be the cause of the fails. Is it possible we aren't passing in a string?

Looks like there was a call to getBody(TRUE) that was missed in the update to Guzzle 5.See #2348365: Update to Guzzle 5 for more info.

Updating to critical as the parent issue is critical.

Added a follow up for converting all instances of getBody(TRUE) to (string) getBody() #2401159: Convert instances of Guzzle getBody(TRUE)

Re-ran composer update zendframework/zend-feed zendframework/zend-stdlib zendframework/zend-escaper