wakusim.env: use latest nwaku Docker image

It should be auto-updated by this CI job:
https://ci.infra.status.im/job/nim-waku/job/docker-latest/

Signed-off-by: Jakub Sokołowski <jakub@status.im>

Author: jakubgs

wakusim.env

@@ -1,5 +1,5 @@
 # Env variables for metal-01.he-eu-hel1.wakusim.misc host.
-NWAKU_IMAGE=wakuorg/nwaku:v0.20.0
+NWAKU_IMAGE=wakuorg/nwaku:latest
 GOWAKU_IMAGE=wakuorg/go-waku:v0.8.0
 # Network scaling.
 NUM_NWAKU_NODES=100