Add check and conversion to String from Array for 'error' in ParseClient (#268)

Added check and conversion to string from Array for 'error' in back4app.com API response

* Add comments to clarify intent of additions

Author: Benjamin Wilson Friedman

src/Parse/ParseClient.php

@@ -372,8 +372,11 @@ public static function _request(
 
         $decoded = json_decode($response, true);
         if (isset($decoded['error'])) {
+            // check to convert error to a string, if an array
+            // used to handle an Array 'error' from back4app.com
+            $errorMessage = is_array($decoded['error']) ? json_encode($decoded['error']) : $decoded['error'];
             throw new ParseException(
-                $decoded['error'],
+                $errorMessage,
                 isset($decoded['code']) ? $decoded['code'] : 0
             );
         }