Update gateway.txt

Some additional gateways; there used to be more, but they have been offline for some time now.

Question: doesn't the main gateway `ipfs.io` need to be `https://ipfs.io/ipfs/@

www/gateway.txt

@@ -3,4 +3,7 @@ https://gateway.ipfs.io/ipfs/@
 https://ipfs.infura.io/ipfs/@
 https://siderus.io/ipfs/@
 https://ipfs.jes.xxx/ipfs/@
-https://www.eternum.io/ipfs/@
+https://www.eternum.io/ipfs/@
+https://xmine128.tk/ipfs/@
+https://hardbin.com/ipfs/@
+https://ipfs.wa.hle.rs/ipfs/@