Link to GEOS manual is broken

[cengel]

The link to GEOS Manual is (http://geos.osgeo.org/doxygen/) in the setup instructions(https://github.com/datacarpentry/geospatial-workshop/blob/gh-pages/setup.md) generates 404 -- I am afraid I don't seem to find any link to replace it with.

[jonjab]

This issue is null. That link disappeared some time ago.