Fix tests

Kind 0.8 has compatibility problems when using older node images.
This forces Kind to use the v1.18.2 image built using Kind 0.8,
fixing the tests.

Without this, you may find that CoreDNS crashes continuously,
resulting in CouchDB nodes not being able to discover each other.

test/e2e-kind.sh

@@ -5,9 +5,9 @@ set -o nounset
 set -o pipefail
 
 readonly CT_VERSION=v3.0.0-rc.1
-readonly KIND_VERSION=v0.7.0
+readonly KIND_VERSION=v0.8.0
 readonly CLUSTER_NAME=chart-testing
-readonly K8S_VERSION=v1.17.0
+readonly K8S_VERSION=v1.18.2@sha256:7b27a6d0f2517ff88ba444025beae41491b016bc6af573ba467b70c5e8e0d85f
 
 run_ct_container() {
     echo 'Running ct container...'