Ensure nav links display active styles on subpaths

[LanesGood]

As described by @smwingo in slack:

noticing that if i click on "explore" and it defaults to the "campaign" part of explore page, the "explore" word in the top menu stays bold/underlined....but if i click for any of the other "explore" pages (platforms, instruments, data prods) that top "explore" word is in same text as rest of top menu

Campaigns

Data Products

Solution:

The logic for determining "Explore" active styles should include subpaths.