Update index.md in roadmap to point to the release page for 3.10
Update index.md in roadmap to point to the release page for 3.10

The release 3.10 page is correctly pointing to the Projects in our github repository, the link here points to the milestone. Hence correcting the same to reflect the redirection right.
gluster/glusterweb,gluster/glusterweb,gluster/glusterweb,gluster/glusterweb