Update Knot.

Dockerfile

 # hadolint ignore=DL3007
-FROM registry.hub.docker.com/cznic/knot:latest
+FROM registry.hub.docker.com/cznic/knot:3.0
 # hadolint ignore=DL3008
 RUN apt-get update && \
     DEBIAN_FRONTEND=noninteractive apt-get install -y --no-install-recommends \