The name of ANT jars have changed. So i had to take the new want named "worklight-ant-deployer.jar" instead of "worklight-ant.jar" in my xml config file.
<taskdef resource="com/worklight/ant/defaults.properties">
<classpath>
<fileset dir="${worklight.server.install.dir}/WorklightServer">
<include name="worklight-ant-deployer.jar"/>
</fileset>
</classpath>
</taskdef>