This is the past future. You are describing something in the past, and referring to something that is in the future at that point in time.
In your case, the word "Will" is correct. This is because 2018 hasn't happened yet. Either word can be correct. See Tᴚoɯɐuo's answer.
You would use the word "would" when you are describing something that was in the future at that point in time, but has passed since then.
Last September we decided that we would meet again at christmas.
Last September we decided that we will meet again at christmas.
The first sentence is referring a christmas which was in the future, but is now in the past. The second sentence is referring to a christmas which is still in the future.