[docs] fix missing code quote on class name for Twitter Firehose sour…

…ce (apache#2800)

site2/docs/io-overview.md

@@ -36,4 +36,4 @@ The following connectors are currently available for Pulsar:
 |[Kafka sink](https://kafka.apache.org)|[`org.apache.pulsar.io.kafka.KafkaSink`](https://github.com/apache/pulsar/blob/master/pulsar-io/kafka/src/main/java/org/apache/pulsar/io/kafka/KafkaStringSink.java)|[Documentation](io-kafka.md#sink)|
 |[Kinesis sink](https://aws.amazon.com/kinesis/)|[`org.apache.pulsar.io.kinesis.KinesisSink`](https://github.com/apache/pulsar/blob/master/pulsar-io/kinesis/src/main/java/org/apache/pulsar/io/kinesis/KinesisSink.java)|[Documentation](io-kinesis.md#sink)|
 |[RabbitMQ source](https://www.rabbitmq.com)|[`org.apache.pulsar.io.rabbitmq.RabbitMQSource`](https://github.com/apache/pulsar/blob/master/pulsar-io/rabbitmq/src/main/java/org/apache/pulsar/io/rabbitmq/RabbitMQSource.java)|[Documentation](io-rabbitmq.md#sink)|
-|[Twitter Firehose source](https://developer.twitter.com/en/docs)|[org.apache.pulsar.io.twitter.TwitterFireHose](https://github.com/apache/pulsar/blob/master/pulsar-io/twitter/src/main/java/org/apache/pulsar/io/twitter/TwitterFireHose.java)|[Documentation](io-twitter.md#source)|
+|[Twitter Firehose source](https://developer.twitter.com/en/docs)|[`org.apache.pulsar.io.twitter.TwitterFireHose`](https://github.com/apache/pulsar/blob/master/pulsar-io/twitter/src/main/java/org/apache/pulsar/io/twitter/TwitterFireHose.java)|[Documentation](io-twitter.md#source)|