title: Gobblin JSON to Avro convert failed with not a Json Array error
body: <p>I'm new to Gobblin and trying to read JSON Kafka message and convert it to AVRO then store it in HDFS. My current job file is like a blow:</p>
  
  <pre><code>job.name=GobblinKafkaQuickStart
  job.group=GobblinKafka
  job.description=Gobblin quick start job for Kafka
  job.lock.enabled=false
  
  kafka.brokers=localhost:9092
  
  source.class=org.apache.gobblin.source.extractor.extract.kafka.KafkaSimpleSource
  extract.namespace=org.apache.gobblin.extract.kafka
  converter.classes=org.apache.gobblin.converter.json.JsonStringToJsonIntermediateConverter, org.apache.gobblin.converter.avro.JsonIntermediateToAvroConverter
  
  
  source.schema=[{"columnName":"name", "dataType":{"type": "string"}}, {"columnName":"city", "dataType":{"type": "string"}}, {"columnName":"age", "dataType":{"type": "integer"}}, {"columnName":"ubdated_at", "dataType":{"type": "string"}}]
  
  
  writer.builder.class=org.apache.gobblin.writer.AvroDataWriterBuilder
  extract.namespace=gobblin.source.extractor.filebased
  gobblin.converter.schemaInjector.schema=SCHEMA
  # writer.file.path.type=tablename
  writer.destination.type=HDFS
  writer.output.format=text
  
  data.publisher.type=org.apache.gobblin.publisher.BaseDataPublisher
  
  mr.job.max.mappers=1
  
  metrics.reporting.file.enabled=true
  metrics.log.dir=${gobblin.cluster.work.dir}/metrics
  metrics.reporting.file.suffix=txt
  
  bootstrap.with.offset=earliest
  </code></pre>
  
  <p>Example Kafka Massage: <code>{"age": 36, "city": "London", "name": "John", "ubdated_at": "2020-05-19"}</code>
  However when I run this on standalone mode, getting bellow error.</p>
  
  <pre><code>ERROR [TaskExecutor-1] org.apache.gobblin.runtime.Task 551 - Task 
  task_GobblinKafkaQuickStart_1589884160573_0 failed java.lang.IllegalStateException: This is not a JSON
  Array. at com.google.gson.JsonElement.getAsJsonArray(JsonElement.java:106) at
  org.apache.gobblin.converter.json.JsonStringToJsonIntermediateConverter.convertSchema(JsonStringToJsonIn
  termediateConverter.java:71) at
  org.apache.gobblin.converter.json.JsonStringToJsonIntermediateConverter.convertSchema(JsonStringToJsonIn
  termediateConverter.java:48) at
  org.apache.gobblin.instrumented.converter.InstrumentedConverterDecorator.convertSchema(InstrumentedConve
  rterDecorator.java:79) at
  org.apache.gobblin.runtime.MultiConverter.convertSchema(MultiConverter.java:76) at
  org.apache.gobblin.runtime.Task.runSynchronousModel(Task.java:417) at
  org.apache.gobblin.runtime.Task.run(Task.java:368) at org.apache.gobblin.runtime.TaskExecutor$TrackingTask.run(TaskExecutor.java:443) at
  org.apache.gobblin.util.executors.MDCPropagatingRunnable.run(MDCPropagatingRunnable.java:39) at
  java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) at
  java.util.concurrent.FutureTask.run(FutureTask.java:266) at
  java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) at
  java.util.concurrent.FutureTask.run(FutureTask.java:266) at
  java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) at
  java.util.concurrent.FutureTask.run(FutureTask.java:266) at
  java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$201(ScheduledThreadPoolExecutor.java:180) at
  java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:293) at 
  java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) at
  java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) at
  java.lang.Thread.run(Thread.java:748)
  </code></pre>
  
  <p>Could some one help me?</p>