Minecraft 1.8 will be released at Tuesday!
We won't be able to update the server right after the release.
So to play on the server you need to have version 1.7.*
As soon as spigot updates we will update the server.
This will only be a client side update as there will be no new 1.8 features. (There might be a few)
When bukkit updates we will be able to fully update the server and have all new features available.
Here you can read all bout the update: Mojang.com