[landing] Give the social icons a little more room at lower breakpoints

Summary: Noticed that the social icons were a little crammed at the smaller breakpoints. Just fixing this up really quick before bringing back their hover state.

Test Plan:
Here's how it looks on iPhone 13 mini:

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

Reviewed By: palys-swm, ashoat

Subscribers: ashoat, Adrian, karol-bisztyga

Differential Revision: https://phabricator.ashoat.com/D3404