chore(ci): update to new k6 docker image

.gitlab-ci.yml

@@ -35,7 +35,7 @@ variables:
   script:
     - API_DOMAIN=$(cat $API_DOMAIN_PATH)
     - terraform/environments/scripts/wait-for-ssl.sh "https://${API_DOMAIN}"
-    - BASE_URL="https://${API_DOMAIN}/graphql" /tmp/k6 run smoketest/main.js
+    - BASE_URL="https://${API_DOMAIN}/graphql" k6 run smoketest/main.js
     # TODO should/could we roll back the service to the last working revision on test failure?
 
 cache_lint: