GEOS-Chem submod update: Merge PR #2225 (Don't expect / in photolysis…

… dirs)

This commit informs the GCHP superproject about the following
commits that were pushed to the GitHub geoschem/geos-chem repository:

a18588576 Merge PR 2225# (Don't expect photolysis dirs to end in "/")

This PR makes removes the requirement that the paths to files containing
photolysis configuration need to end with a "/" character.  This will
facilitate connecting GEOS-Chem to external models like CESM.

Signed-off-by: Bob Yantosca <yantosca@seas.harvard.edu>