[docs] fix missing code quote on class name for Twitter Firehose source (#2800)
[docs] fix missing code quote on class name for Twitter Firehose source (#2800)


nkurihar/pulsar,massakam/pulsar,jai1/pulsar,jai1/pulsar,yahoo/pulsar,massakam/pulsar,ArvinDevel/incubator-pulsar,merlimat/pulsar,nkurihar/pulsar,merlimat/pulsar,merlimat/pulsar,jai1/pulsar,yahoo/pulsar,jai1/pulsar,nkurihar/pulsar,yahoo/pulsar,nkurihar/pulsar,merlimat/pulsar,jai1/pulsar,ArvinDevel/incubator-pulsar,ArvinDevel/incubator-pulsar,ArvinDevel/incubator-pulsar,ArvinDevel/incubator-pulsar,nkurihar/pulsar,massakam/pulsar,nkurihar/pulsar,nkurihar/pulsar,merlimat/pulsar,yahoo/pulsar,massakam/pulsar,yahoo/pulsar,jai1/pulsar,ArvinDevel/incubator-pulsar,ArvinDevel/incubator-pulsar,jai1/pulsar,massakam/pulsar,nkurihar/pulsar,merlimat/pulsar,ArvinDevel/incubator-pulsar,jai1/pulsar,yahoo/pulsar,nkurihar/pulsar,massakam/pulsar,jai1/pulsar