add content-type to uploads

src/memes.ts

@@ -65,7 +65,8 @@ export default async function memeService(baseLog: Logger, prisma: PrismaClient,
 
     async function persist(m: Meme) {
         const index = meili.index('memes')
-        return index.updateDocuments([m])
+        const doc = ({ ...m, postedAt: m.postedAt.valueOf() })
+        return index.updateDocuments([doc])
     }
 
     await ensureMeiliIndex();