Get rid of nasty error on first startup when in standalone mode

[simplesteph]

Error below:

[2017-04-27 22:55:18,729] ERROR CRITICAL: Failed to deserialize offset data when getting offsets for task with namespace GitHubSourceConnectorDemo-2. No value for this data will be returned, which may break the task or cause it to skip some data. This could either be due to an error in the connector implementation or incompatible schema. (org.apache.kafka.connect.storage.OffsetStorageReaderImpl:102)
org.apache.kafka.connect.errors.DataException: JsonConverter with schemas.enable requires "schema" and "payload" fields and may not contain additional fields. If you are trying to deserialize plain JSON data, set schemas.enable=false in your converter configuration.
        at org.apache.kafka.connect.json.JsonConverter.toConnectData(JsonConverter.java:309)
        at org.apache.kafka.connect.storage.OffsetStorageReaderImpl.offsets(OffsetStorageReaderImpl.java:96)
        at org.apache.kafka.connect.storage.OffsetStorageReaderImpl.offset(OffsetStorageReaderImpl.java:54)
        at com.simplesteph.kafka.GitHubSourceTask.initializeLastVariables(GitHubSourceTask.java:57)
        at com.simplesteph.kafka.GitHubSourceTask.start(GitHubSourceTask.java:52)
        at org.apache.kafka.connect.runtime.WorkerSourceTask.execute(WorkerSourceTask.java:141)
        at org.apache.kafka.connect.runtime.WorkerTask.doRun(WorkerTask.java:139)
        at org.apache.kafka.connect.runtime.WorkerTask.run(WorkerTask.java:182)
        at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
        at java.util.concurrent.FutureTask.run(FutureTask.java:266)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
        at java.lang.Thread.run(Thread.java:745)

Connector still works, and the error disappears after some offsets have been first committed. PR welcome