If anyone facing problem with eclipse(Oxygen), this answer is for those.
Help --> Install New Software-->
place this URL in work with field
Eclipse Oxygen: http://download.eclipse.org/releases/oxygen/
Eclipse Photon: http://download.eclipse.org/releases/photon/
Select the list of software's which do you want to update and complete normal update process. Once, installation completed you have to restart the eclipse. So, you are able to create the Dynamic Web Project.
Thanks,