Bump version constraint for Graticule #35

collectiveidea/graticule@5a2b604

Gracticule 2.4.0 doesn't raise custom error messages due to the minor mistake above. Would be sweet to bump the version constraint to 2.5 (given everything still works) where this has been removed.

Also opened an issue on Graticule to release a minor or patch version to fix this that you could then allow. So that would be equally as cool thanks!