A malformed message crashes the connector

Summary: When following the [kafka connect quickstart|https://docs.couchbase.com/kafka-connector/3.4/quickstart.html], everything works okay until an improperly formatted message is put into the kafka topic.

Repro:

1. Follow the quick start for using Couchbase as a sink.
2. The 'mvn compile exec:java" step should work correctly, and you should end up with 20 documents in a Couchbase bucket.
3. Send a message to the topic that is not{{ JSON. For example: bin\windows\kafka-console-producer.bat --broker-list localhost:9092 --topic test-default and then enter a message like "foobar"}}

Actual: An error will occur like: [2019-04-04 10:43:57,908] ERROR WorkerSinkTask{id=home-delivery-sink-1} Task is being killed and will not recover until manually restarted (org.apache.kafka.connect.runtime.WorkerTask)

Expected: Almost anything other than crashing and not continuing to process other messages. For instance, it could save the message as a binary document in Couchbase. It could report an error but then skip/ignore the message. In a situation where only well-formed messages get into Kafka, everything is fine. But right now, even one malformed/mistake message shuts the whole connector down.