Fix legacy handshake with hostnames that include IP addresses (#571)

proxy/src/main/java/com/velocitypowered/proxy/connection/backend/VelocityServerConnection.java

@@ -122,7 +122,7 @@ public class VelocityServerConnection implements MinecraftConnectionAssociation,
             .orElseGet(() -> registeredServer.getServerInfo().getAddress())
             .getHostString())
         .append('\0')
-        .append(proxyPlayer.getRemoteAddress().getHostString())
+        .append(proxyPlayer.getRemoteAddress().getAddress().getHostAddress())
         .append('\0')
         .append(proxyPlayer.getGameProfile().getUndashedId())
         .append('\0');