Update ubuntu ami version (#547)

Mike Terhar · web-flow · commit e7452206b33a · 2021-08-16T08:56:17.000-05:00
The 1804 ami is unsupported.
diff --git a/setup/kubernetes/aws.md b/setup/kubernetes/aws.md
@@ -179,7 +179,7 @@ as a workspace deployment option, you'll need to
 
    nodeGroups:
      - name: coder-node-group
-       amiFamily: Ubuntu1804
+       amiFamily: Ubuntu2004
    ```
 
 1. Create your nodegroup (be sure to provide the correct file name):
