avatar: bump cache-control expiry to 12h

Signed-off-by: Anirudh Oppiliappan <[e-mail]>

avatar/src/index.js

···
 			response = new Response(avatarData, {
 				headers: {
 					'Content-Type': contentType,
-					'Cache-Control': 'public, max-age=3600',
+					'Cache-Control': 'public, max-age=43200', // 12 h
 				},
 			});