Fix patch link in zeroc-ice34 formula

This PR should
- have a green Travis status for all the tested components
- turn [OMERO-homebrew-develop](http://hudson.openmicroscopy.org.uk/job/OMERO-homebrew-develop/) and [OMERO-homebrew-stable](http://hudson.openmicroscopy.org.uk/job/OMERO-homebrew-stable/) green by fixing the default zeroc-ice34 formula.


More generally, do we want to find an alternate location for these patches if the forum URL evolves again?