update social media card image

[MoralCode]

seems as though theres an outdated homepage.jpg image being used on this line

FindYourVaccine.org/_includes/head.html

Line 21 in 412483d

<meta property="og:image" content="{{ site.url }}/assets/img/homepage.jpg" />

from a quick search it seems like this is where the "card image" that appears on social media link previews is set, so it may be nice to either

1. take a new screenshot of the homepage to replace this old onr
2. design a new image (sorta like the angry birds one in the link above) with social media in mind
3. take a version of the favicon logo and use it for this
4. or something else