Update broken link to mx project.

mx project is deprecated now. Dunno if we should mention that.

Signed-off-by: Anurag Priyam <anurag08priyam@gmail.com>
Update link: ete.cgenomics.org -> etetoolkit.org.

Signed-off-by: Anurag Priyam <anurag08priyam@gmail.com>