[landing] Re-introduce hover styling for Footer links

Summary:
Bring back the hover styling from before. Here's how it looks:

Test Plan: NA, looks as expected

Reviewers: def-au1t, palys-swm, varun, benschac, ashoat

Reviewed By: palys-swm, ashoat

Subscribers: ashoat, Adrian, karol-bisztyga

Differential Revision: https://phabricator.ashoat.com/D3366