Hope you are doing well.
It seems the custom jars are not getting loaded into flume.
Please try with below solution
-edit flume.conf file and change TwitterAgent.sources.Twitter.type to
TwitterAgent.sources.Twitter.type = com.cloudera.flume.source.TwitterSource
also uncomment FLUME_CLASSPATH from flume-env.sh make sure you have necessary jars to run the flume.
Now go to /usr/lib/flume-ng/apache-flume-1.4.0-bin/bin and execute command
./flume-ng agent -c conf -f /usr/lib/flume-ng/apache-flume-1.4.0-bin/conf/flume.conf -n TwitterAgent
Please try this solution and let us know if you face any issue so we can help you out here.