S3 PutBucketPolicy fixed

[byterock]

This call returns only json so made this change to Paws::Net::RestXMLResponse

sub response_to_object

+        $unserialized_struct = {};
+      } elsif (exists($headers->{'content-type'})
+                      and $headers->{'content-type'} eq 'application/json'
+                  and $ret_class->can('_payload')){
+        $unserialized_struct->{$ret_class->_payload} = $content;
+         } else {

https://github.com/byterock/aws-sdk-perl/tree/s3ObjectTagging

no boto changes