Changed pom file to work with Twitter4j 4.0.X api

Hi,

Currently Twitter exposes a different API than those days. Also Twitter4J has also changed accordingly. 
But since WSO2-Twitter Connector depends on the old library at orbit, it's not capable doing all the things mentioned in the document.
This change is to get the latest Twitter4J (4.0.x series) from their repository and pack with Twitter Connector.

Thanks!