2.1.0
* prepare for 4.1 * Update stubs/RdKafka/KafkaErrorException.php Co-authored-by: Karol Wnuk <k.wnuk@op.pl> * Update .travis.yml * fix and improve tests * use flush * remove const aliases * only use transactional producer where needed * fix const naming Co-authored-by: Karol Wnuk <k.wnuk@op.pl>