fix vercel output routing (#60)

Author: brookslybrand

vercel/vercel/output/config.json

@@ -7,11 +7,14 @@
     },
     {
       "src": "/assets/(.*)",
-      "dest": "/assets/$1"
+      "dest": "/assets/$1",
+      "headers": {
+        "Cache-Control": "public, max-age=31536000, immutable"
+      }
     },
     {
       "src": "/(.*)",
-      "dest": "/"
+      "dest": "/$1"
     }
   ]
 }