Fix ScienceAlert to not be stuck on 1.8rc2

This should allow users affected by https://github.com/KSP-CKAN/CKAN-meta/issues/196 to update to 1.8.4 by reinstalling ScienceAlert. 1.8rc1 is no longer listed however it is reasonably out of date (October 20) and 1.8.1 is the final version for 0.25