Update producer to use push() instead of send() due to updated kafka-rb
Update producer to use push() instead of send() due to updated kafka-rb

See: https://github.com/acrosa/kafka-rb/commit/37cf16f1c5ae4b643866fd812b6cf0580c20a41d

ops-baidu/fluent-plugin-kafka,ops-baidu/fluent-plugin-kafka